Cache Management Operations Using Streaming Engine

ABSTRACT

A stream of data is accessed from a memory system using a stream of addresses generated in a first mode of operating a streaming engine in response to executing a first stream instruction. A block cache management operation is performed on a cache in the memory using a block of addresses generated in a second mode of operating the streaming engine in response to executing a second stream instruction.

TECHNICAL FIELD

This relates to using a streaming engine to perform block-oriented cachemaintenance and cache preloading.

BACKGROUND

Digital signal processors (DSP) are optimized for processing streams ofdata that may be derived from various input signals, such as sensordata, a video stream, a voice channel, radar signals, biomedicalsignals, etc. Digital signal processors operating on real-time datatypically receive an input data stream, perform a filter function on thedata stream (such as encoding or decoding) and output a transformed datastream. The system is called real-time because the application fails ifthe transformed data stream is not available for output when scheduled.Typical video encoding requires a predictable but non-sequential inputdata pattern. A typical application requires memory access to load dataregisters in a data register file and then supply data from the dataregisters to functional units which perform the data processing.

One or more DSP processing cores can be combined with various peripheralcircuits, blocks of memory, etc. on a single integrated circuit (IC) dieto form a system on chip (SoC). These systems can include multipleinterconnected processors that share the use of on-chip and off-chipmemory. A processor can include some combination of instruction cache(ICache) and data cache (DCache) to improve processing. Furthermore,multiple processors with shared memory can be incorporated in a singleembedded system. The processors can physically share the same memorywithout accessing data or executing code located in the same memorylocations or can use some portion of the shared memory as common sharedmemory.

SUMMARY

Methods and apparatus are provided such that a stream of data can beaccessed from a memory system using a first stream of addressesgenerated in a first mode of operating a streaming engine in response toexecuting a first stream instruction. A block cache management operationcan be performed on a cache in the memory system using a second streamof addresses generated in a second mode of operating the streamingengine in response to executing a second stream instruction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example dual scalar/vector data path processor.

FIG. 2 illustrates the registers and functional units in the dualscalar/vector data path processor illustrated in FIG. 1.

FIG. 3 illustrates a global scalar register file.

FIG. 4 illustrates a local scalar register file shared by arithmeticfunctional units.

FIG. 5 illustrates a local scalar register file shared by multiplyfunctional units.

FIG. 6 illustrates a local scalar register file shared by load/storeunits.

FIG. 7 illustrates a global vector register file.

FIG. 8 illustrates a predicate register file.

FIG. 9 illustrates a local vector register file shared by arithmeticfunctional units.

FIG. 10 illustrates a local vector register file shared by multiply andcorrelation functional units.

FIG. 11 illustrates pipeline phases of a processing unit.

FIG. 12 illustrates sixteen instructions of a single fetch packet.

FIG. 13 illustrates an example of the instruction coding ofinstructions.

FIG. 14 illustrates bit coding of a condition code extension slot 0.

FIG. 15 illustrates bit coding of a condition code extension slot 1.

FIG. 16 illustrates bit coding of a constant extension slot 0.

FIG. 17 is a partial block diagram illustrating constant extension.

FIG. 18 illustrates carry control for SIMD operations.

FIG. 19 illustrates a conceptual view of streaming engines.

FIG. 20 illustrates a sequence of formatting operations.

FIG. 21 illustrates an example of lane allocation in a vector.

FIG. 22 illustrates an example of lane allocation in a vector.

FIG. 23 illustrates a basic two-dimensional (2D) stream.

FIG. 24 illustrates the order of elements within the example stream ofFIG. 23.

FIG. 25 illustrates extracting a smaller rectangle from a largerrectangle.

FIG. 26 illustrates how an example streaming engine fetches a streamwith a transposition granularity of 4 bytes.

FIG. 27 illustrates how an example streaming engine fetches a streamwith a transposition granularity of 8 bytes.

FIG. 28 illustrates the details of an example streaming engine.

FIG. 29 illustrates an example stream template register.

FIG. 30 illustrates sub-field definitions of the flags field of theexample stream template register of FIG. 29.

FIG. 31 illustrates an example of a vector length masking/groupduplication block.

FIG. 32 is a partial schematic diagram of an example of the generationof the stream engine valid or invalid indication.

FIG. 33 is a partial schematic diagram of a streaming engine addressgenerator illustrating generation of the loop address and loop count.

FIG. 34 illustrates a partial schematic diagram showing the streamingengine supply of data of this example.

FIG. 35 illustrates a partial schematic diagram showing the streamingengine supply of valid data to the predicate unit.

FIG. 36 is a block diagram of a multiprocessor system with multiplelevels of cache.

FIG. 37 is a partial schematic diagram for cache management operationsusing the streaming engine of FIG. 28.

FIG. 38 is a flow chart illustrating operation of cache managementoperations using the streaming engine.

DETAILED DESCRIPTION

In the drawings, like elements are denoted by like reference numeralsfor consistency.

Digital signal processors (DSP) are optimized for processing streams ofdata that may be derived from various input signals, such as sensordata, a video stream, a voice channel, radar signals, biomedicalsignals, etc. Memory bandwidth and scheduling are concerns for digitalsignal processors operating on real-time data. An example DSP processingcore is described herein that includes a streaming engine to improvememory bandwidth and data scheduling.

One or more DSP processing cores can be combined with various peripheralcircuits, blocks of memory, etc. on a single integrated circuit (IC) dieto form a system on chip (SoC). See, for example, “66AK2Hx MulticoreKeystone™ DSP+ARM® System-on-Chip,” 2013 which is incorporated byreference herein.

In the example DSP core described herein, an autonomous streaming engine(SE) is coupled to the DSP. In this example, the streaming engineincludes two closely coupled streaming engines that can manage two datastreams simultaneously. In another example, the streaming engine iscapable of managing only a single stream, while in other examples thestreaming engine is capable of handling more than two streams. In eachcase, for each stream, the streaming engine includes an addressgeneration stage, a data formatting stage, and some storage forformatted data waiting for consumption by the processor. In the examplesdescribed herein, addresses are derived from algorithms that can involvemulti-dimensional loops, each dimension maintaining an iteration count.In one example, the streaming engine supports six levels of nestediteration. In other examples, more or fewer levels of iteration aresupported.

In this example, the DSP data processing systems employs data caches andinstruction caches to improve performance. A small amount of high-speedmemory is used for each cache. These cache memories are filled from mainmemory on an as-needed basis. When the data processor requires data oran instruction, this is first sought from the respective cache memory.If the data or instruction sought is already stored in the cache memory,it is recalled faster than it could have been recalled from main memory.If the data or instruction sought is not stored in the cache memory, itis recalled from main memory for use and stored in the correspondingcache. A performance improvement is achieved using cache memory basedupon the principle of locality of reference. It is likely that the dataor the instruction just sought by the data processor will be neededagain soon. Use of cache memories speeds the accesses needed to servicethese future needs.

It is desirable to provide a level of control to the programmer overcache operations. In this example, the cache system supports a writebackmechanism, whereby the programmer can direct the cache to write data inthe cache back to external memory for shared access by another processorwhich doesn't have access to the cache. Similarly, it is often desirableto be able to clear or invalidate cache entries so that new data can beaccessed at addresses which have been updated in the reference memory.

In this example, in addition to its core data stream support, thestreaming engine supports a range of special “data-less” streams. Adata-less stream may be used move data between various levels of cacheand memory, without bringing data to the processor. In this example, twospecial instructions are provided to allow a program to initiate adata-less stream. A block cache maintenance operation is initiated by a“BLKCMO” instruction. A block cache preload operation is initiated witha “BLKPLD” instruction.

An example of performing block-oriented cache maintenance operations andblock oriented cache preloading using BLKCMO and BLKPLD instructions isdescribed in more detail with regard to FIGS. 36-38.

An example DSP processor is described in detail herein with reference toFIGS. 1-18. An example streaming engine capable of managing two datastreams using six-dimensional nested loops is described in detail hereinwith reference to FIGS. 19-35.

FIG. 1 illustrates an example processor 100 that includes dualscalar/vector data paths 115, 117. Processor 100 includes a streamingengine 125 that is described in more detail herein. Processor 100includes separate level one instruction cache (L1I) 121 and level onedata cache (L1D) 123. Processor 100 includes a level 2 (L2) combinedinstruction/data cache 130 that holds both instructions and data. FIG. 1illustrates connection between L1I cache and L2 combinedinstruction/data cache 130, 512-bit bus 142. FIG. 1 illustrates theconnection between L1D cache 123 and L2 combined instruction/data cache130, 512-bit bus 145. In the example processor 100, L2 combinedinstruction/data cache 130 stores both instructions to back up L1I cache121 and data to back up L1D cache 123. In this example, L2 combinedinstruction/data cache 130 is further connected to higher level cacheand/or main memory using known or later developed memory systemtechniques not illustrated in FIG. 1. As used herein, the term “higherlevel” memory or cache refers to a next level in a memory hierarchy thatis more distant from the processor, while the term “lower level” memoryor cache refers to a level in the memory hierarchy that is closer to theprocessor. L1I cache 121, L1D cache 123, and L2 cache 130 may beimplemented in different sizes in various examples. In this example, L1Icache 121 and L1D cache 123 are each 32K bytes, and L2 cache 130 is1024K bytes. In the example processor 100, L1I cache 121, L1D cache 123and L2 combined instruction/data cache 130 are formed on a singleintegrated circuit. This single integrated circuit optionally includesother circuits.

Processing unit core 110 fetches instructions from L1I cache 121 ascontrolled by instruction fetch unit 111. Instruction fetch unit 111determines the next instructions to be executed and recalls a fetchpacket sized set of such instructions. The nature and size of fetchpackets are further detailed below. Instructions are directly fetchedfrom L1I cache 121 upon a cache hit if the instructions are stored inL1I cache 121. Upon a cache miss occurring when the specifiedinstructions are not stored in L1I cache 121, the instructions aresought in L2 combined cache 130. In this example, the size of a cacheline in L1I cache 121 equals the size of a fetch packet which is 512bits. The memory locations of these instructions are either a hit in L2combined cache 130 or a miss. A hit is serviced from L2 combined cache130. A miss is serviced from a higher level of cache (not illustrated)or from main memory (not illustrated). In this example, the requestedinstruction is simultaneously supplied to both L1I cache 121 andprocessing unit core 110 to speed use.

In this example, processing unit core 110 includes multiple functionalunits to perform instruction specified data processing tasks.Instruction dispatch unit 112 determines the target functional unit ofeach fetched instruction. In this example, processing unit 110 operatesas a very long instruction word (VLIW) processor capable of operating onmultiple instructions in corresponding functional units simultaneously.A complier organizes instructions in execute packets that are executedtogether. Instruction dispatch unit 112 directs each instruction to itstarget functional unit. The functional unit assigned to an instructionis completely specified by the instruction produced by the compiler. Thehardware of processing unit core 110 has no part in the functional unitassignment. In this example, instruction dispatch unit 112 operates onseveral instructions in parallel. The number of such parallelinstructions is set by the size of the execute packet. This is furtherdescribed herein.

One part of the dispatch task of instruction dispatch unit 112 isdetermining whether the instruction is to execute on a functional unitin scalar data path side A 115 or vector data path side B 116. Aninstruction bit within each instruction called the s bit determineswhich data path the instruction controls. This is further describedherein.

Instruction decode unit 113 decodes each instruction in a currentexecute packet. Decoding includes identification of the functional unitperforming the instruction, identification of registers used to supplydata for the corresponding data processing operation from among possibleregister files, and identification of the register destination of theresults of the corresponding data processing operation. As furtherexplained below, instructions can include a constant field in place ofone register number operand field. The result of this decoding aresignals for control of the target functional unit to perform the dataprocessing operation specified by the corresponding instruction on thespecified data.

Processing unit core 110 includes control registers 114. Controlregisters 114 store information for control of the functional units inscalar data path side A 115 and vector data path side B 116. Thisinformation may include mode information or the like.

The decoded instructions from instruction decode 113 and informationstored in control registers 114 are supplied to scalar data path side A115 and vector data path side B 116. As a result, functional unitswithin scalar data path side A 115 and vector data path side B 116perform instruction specified data processing operations uponinstruction specified data and store the results in an instructionspecified data register or registers. Each of scalar data path side A115 and vector data path side B 116 include multiple functional unitsthat operate in parallel. These are further described below inconjunction with FIG. 2. There is a data path 117 between scalar datapath side A 115 and vector data path side B 116 permitting dataexchange.

Processing unit core 110 includes further non-instruction-based modules.Emulation unit 118 permits determination of the machine state ofprocessing unit core 110 in response to instructions. This capabilitycan be employed for algorithmic development. Interrupts/exceptions unit119 enables processing unit core 110 to be responsive to external,asynchronous events (interrupts) and to respond to attempts to performimproper operations (exceptions).

Processor 100 includes streaming engine 125. Streaming engine 125supplies two data streams from predetermined addresses cached in L2combined cache 130 to register files of vector data path side B ofprocessing unit core 110. This provides controlled data movement frommemory (as cached in L2 combined cache 130) directly to functional unitoperand inputs. This is further described herein.

FIG. 1 illustrates example data widths of busses between various parts.L1I cache 121 supplies instructions to instruction fetch unit 111 viabus 141. Bus 141 is a 512-bit bus in this example. Bus 141 isunidirectional from L1I cache 121 to processing unit 110. L2 combinedcache 130 supplies instructions to L1I cache 121 via bus 142. Bus 142 isa 512-bit bus in this example. Bus 142 is unidirectional from L2combined cache 130 to L1I cache 121.

L1D cache 123 exchanges data with register files in scalar data pathside A 115 via bus 143. Bus 143 is a 64-bit bus in this example. L1Dcache 123 exchanges data with register files in vector data path side B116 via bus 144. Bus 144 is a 512-bit bus in this example. Busses 143and 144 are illustrated as bidirectional supporting both processing unitcore 110 data reads and data writes. L1D cache 123 exchanges data withL2 combined cache 130 via bus 145. Bus 145 is a 512-bit bus in thisexample. Bus 145 is illustrated as bidirectional supporting cacheservice for both processing unit core 110 data reads and data writes.

Processor data requests are directly fetched from L1D cache 123 upon acache hit (if the requested data is stored in L1D cache 123). Upon acache miss (the specified data is not stored in L1D cache 123), the datais sought in L2 combined cache 130. The memory locations of therequested data are either a hit in L2 combined cache 130 or a miss. Ahit is serviced from L2 combined cache 130. A miss is serviced fromanother level of cache (not illustrated) or from main memory (notillustrated). The requested data may be simultaneously supplied to bothL1D cache 123 and processing unit core 110 to speed use.

L2 combined cache 130 supplies data of a first data stream to streamingengine 125 via bus 146. Bus 146 is a 512-bit bus in this example.Streaming engine 125 supplies data of the first data stream tofunctional units of vector data path side B 116 via bus 147. Bus 147 isa 512-bit bus in this example. L2 combined cache 130 supplies data of asecond data stream to streaming engine 125 via bus 148. Bus 148 is a512-bit bus in this example. Streaming engine 125 supplies data of thissecond data stream to functional units of vector data path side B 116via bus 149, which is a 512-bit bus in this example. Busses 146, 147,148 and 149 are illustrated as unidirectional from L2 combined cache 130to streaming engine 125 and to vector data path side B 116 in accordancewith this example.

Streaming engine data requests are directly fetched from L2 combinedcache 130 upon a cache hit (if the requested data is stored in L2combined cache 130). Upon a cache miss (the specified data is not storedin L2 combined cache 130), the data is sought from another level ofcache (not illustrated) or from main memory (not illustrated). It istechnically feasible in some examples for L1D cache 123 to cache datanot stored in L2 combined cache 130. If such operation is supported,then upon a streaming engine data request that is a miss in L2 combinedcache 130, L2 combined cache 130 snoops L1D cache 123 for the streamengine requested data. If L1D cache 123 stores the data, the snoopresponse includes the data, which is then supplied to service thestreaming engine request. If L1D cache 123 does not store the data, thesnoop response indicates this and L2 combined cache 130 services thestreaming engine request from another level of cache (not illustrated)or from main memory (not illustrated).

In this example, both L1D cache 123 and L2 combined cache 130 can beconfigured as selected amounts of cache or directly addressable memoryin accordance with U.S. Pat. No. 6,606,686 entitled UNIFIED MEMORYSYSTEM ARCHITECTURE INCLUDING CACHE AND DIRECTLY ADDRESSABLE STATICRANDOM ACCESS MEMORY, which is incorporated by reference herein.

In this example, processor 100 is fabricated on an integrated chip (IC)that is mounted on a ball grid array (BGA) substrate. A BGA substrateand IC die together may be referred to as “BGA package,” “IC package,”“integrated circuit,” “IC,” “chip,” “microelectronic device,” or similarterminology. The BGA package may include encapsulation material to coverand protect the IC die from damage. In another example, other types ofknown or later developed packaging techniques may be used with processor100.

FIG. 2 illustrates further details of functional units and registerfiles within scalar data path side A 115 and vector data path side B116. Scalar data path side A 115 includes L1 unit 221, S1 unit 222, M1unit 223, N1 unit 224, D1 unit 225 and D2 unit 226. Scalar data pathside A 115 includes global scalar register file 211, L1/S1 localregister file 212, M1/N1 local register file 213 and D1/D2 localregister file 214. Vector data path side B 116 includes L2 unit 241, S2unit 242, M2 unit 243, N2 unit 244, C unit 245 and P unit 246. Vectordata path side B 116 includes global vector register file 231, L2/S2local register file 232, M2/N2/C local register file 233 and predicateregister file 234. Which functional units can read from or write towhich register files is described in more detail herein.

Scalar data path side A 115 includes L1 unit 221. L1 unit 221 generallyaccepts two 64-bit operands and produces one 64-bit result. The twooperands are each recalled from an instruction specified register ineither global scalar register file 211 or L1/S1 local register file 212.L1 unit 221 performs the following instruction selected operations:64-bit add/subtract operations; 32-bit min/max operations; 8-bit SingleInstruction Multiple Data (SIMD) instructions such as sum of absolutevalue, minimum and maximum determinations; circular min/max operations;and various move operations between register files. The result iswritten into an instruction specified register of global scalar registerfile 211, L1/S1 local register file 212, M1/N1 local register file 213or D1/D2 local register file 214.

Scalar data path side A 115 includes S1 unit 222. S1 unit 222 generallyaccepts two 64-bit operands and produces one 64-bit result. The twooperands are each recalled from an instruction specified register ineither global scalar register file 211 or L1/S1 local register file 212.In this example, S1 unit 222 performs the same type operations as L1unit 221. In another example, there may be slight variations between thedata processing operations supported by L1 unit 221 and S1 unit 222. Theresult is written into an instruction specified register of globalscalar register file 211, L1/S1 local register file 212, M1/N1 localregister file 213 or D1/D2 local register file 214.

Scalar data path side A 115 includes M1 unit 223. M1 unit 223 generallyaccepts two 64-bit operands and produces one 64-bit result. The twooperands are each recalled from an instruction specified register ineither global scalar register file 211 or M1/N1 local register file 213.In this example, M1 unit 223 performs the following instruction selectedoperations: 8-bit multiply operations; complex dot product operations;32-bit bit count operations; complex conjugate multiply operations; andbit-wise Logical Operations, moves, adds and subtracts. The result iswritten into an instruction specified register of global scalar registerfile 211, L1/S1 local register file 212, M1/N1 local register file 213or D1/D2 local register file 214.

Scalar data path side A 115 includes N1 unit 224. N1 unit 224 generallyaccepts two 64-bit operands and produces one 64-bit result. The twooperands are each recalled from an instruction specified register ineither global scalar register file 211 or M1/N1 local register file 213.In this example, N1 unit 224 performs the same type operations as M1unit 223. There are also double operations (called dual issuedinstructions) that employ both the M1 unit 223 and the N1 unit 224together. The result is written into an instruction specified registerof global scalar register file 211, L1/S1 local register file 212, M1/N1local register file 213 or D1/D2 local register file 214.

Scalar data path side A 115 includes D1 unit 225 and D2 unit 226. D1unit 225 and D2 unit 226 generally each accept two 64-bit operands andeach produce one 64-bit result. D1 unit 225 and D2 unit 226 generallyperform address calculations and corresponding load and storeoperations. D1 unit 225 is used for scalar loads and stores of 64 bits.D2 unit 226 is used for vector loads and stores of 512 bits. In thisexample, D1 unit 225 and D2 unit 226 also perform: swapping, pack andunpack on the load and store data; 64-bit SIMD arithmetic operations;and 64-bit bit-wise logical operations. D1/D2 local register file 214stores base and offset addresses used in address calculations for thecorresponding loads and stores. The two operands are each recalled froman instruction specified register in either global scalar register file211 or D1/D2 local register file 214. The calculated result is writteninto an instruction specified register of global scalar register file211, L1/S1 local register file 212, M1/N1 local register file 213 orD1/D2 local register file 214.

Vector data path side B 116 includes L2 unit 241. L2 unit 221 generallyaccepts two 512-bit operands and produces one 512-bit result. The twooperands are each recalled from an instruction specified register ineither global vector register file 231, L2/S2 local register file 232 orpredicate register file 234. In this example, L2 unit 241 performsinstruction similar to L1 unit 221 except on wider 512-bit data. Theresult may be written into an instruction specified register of globalvector register file 231, L2/S2 local register file 232, M2/N2/C localregister file 233 or predicate register file 234.

Vector data path side B 116 includes S2 unit 242. S2 unit 242 generallyaccepts two 512-bit operands and produces one 512-bit result. The twooperands are each recalled from an instruction specified register ineither global vector register file 231, L2/S2 local register file 232 orpredicate register file 234. In this example, S2 unit 242 performsinstructions similar to S1 unit 222. The result is written into aninstruction specified register of global vector register file 231, L2/S2local register file 232, M2/N2/C local register file 233 or predicateregister file 234.

Vector data path side B 116 includes M2 unit 243. M2 unit 243 generallyaccepts two 512-bit operands and produces one 512-bit result. The twooperands are each recalled from an instruction specified register ineither global vector register file 231 or M2/N2/C local register file233. In this example, M2 unit 243 performs instructions similar to M1unit 223 except on wider 512-bit data. The result is written into aninstruction specified register of global vector register file 231, L2/S2local register file 232 or M2/N2/C local register file 233.

Vector data path side B 116 includes N2 unit 244. N2 unit 244 generallyaccepts two 512-bit operands and produces one 512-bit result. The twooperands are each recalled from an instruction specified register ineither global vector register file 231 or M2/N2/C local register file233. In this example, N2 unit 244 performs the same type operations asM2 unit 243. There are also double operations (called dual issuedinstructions) that employ both M2 unit 243 and the N2 unit 244 together.The result is written into an instruction specified register of globalvector register file 231, L2/S2 local register file 232 or M2/N2/C localregister file 233.

Vector data path side B 116 includes correlation (C) unit 245. C unit245 generally accepts two 512-bit operands and produces one 512-bitresult. The two operands are each recalled from an instruction specifiedregister in either global vector register file 231 or M2/N2/C localregister file 233. In this example, C unit 245 performs “Rake” and“Search” instructions that are used for WCDMA (wideband code divisionmultiple access) encoding/decoding. In this example, C unit 245 canperform up to 512 multiples per clock cycle of a 2-bit PN (pseudorandomnumber) and 8-bit I/Q (complex number), 8-bit and 16-bitSum-of-Absolute-Difference (SAD) calculations, up to 512 SADs per clockcycle, horizontal add and horizontal min/max instructions, and vectorpermutes instructions. C unit 245 also contains 4 vector controlregisters (CUCR0 to CUCR3) used to control certain operations of C unit245 instructions. Control registers CUCR0 to CUCR3 are used as operandsin certain C unit 245 operations. In some examples, control registersCUCR0 to CUCR3 are used in control of a general permutation instruction(VPERM), and as masks for SIMD multiple DOT product operations (DOTPM)and SIMD multiple Sum-of-Absolute-Difference (SAD) operations. Infurther examples, control register CUCR0 is used to store thepolynomials for Galois Field Multiply operations (GFMPY) and controlregister CUCR1 is used to store the Galois field polynomial generatorfunction.

Vector data path side B 116 includes P unit 246. Vector predicate (P)unit 246 performs basic logic operations on registers of local predicateregister file 234. P unit 246 has direct access to read from and writeto predication register file 234. The logic operations include singleregister unary operations such as NEG (negate) which inverts each bit ofthe single register, BITCNT (bit count) which returns a count of thenumber of bits in the single register having a predetermined digitalstate (1 or 0), RMBD (right most bit detect) which returns a number ofbit positions from the least significant bit position (right most) to afirst bit position having a predetermined digital state (1 or 0),DECIMATE which selects every instruction specified Nth (1, 2, 4, etc.)bit to output, and EXPAND which replicates each bit an instructionspecified N times (2, 4, etc.). The logic operations also include tworegister binary operations such as AND which is a bitwise AND of data ofthe two registers, NAND which is a bitwise AND and negate of data of thetwo registers, OR which is a bitwise OR of data of the two registers,NOR which is a bitwise OR and negate of data of the two registers, andXOR which is exclusive OR of data of the two registers. The logicoperations include transfer of data from a predicate register ofpredicate register file 234 to another specified predicate register orto a specified data register in global vector register file 231. One useof P unit 246 is manipulation of the SIMD vector comparison results foruse in control of a further SIMD vector operation. The BITCNTinstruction can be used to count the number of 1's in a predicateregister to determine the number of valid data elements from a predicateregister.

FIG. 3 illustrates global scalar register file 211. There are 16independent 64-bit wide scalar registers designated A0 to A15. Eachregister of global scalar register file 211 can be read from or writtento as 64-bits of scalar data. All scalar data path side A 115 functionalunits (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225and D2 unit 226) can read or write to global scalar register file 211.Global scalar register file 211 can be read from as 32-bits or as64-bits and written to as 64-bits. The instruction executing determinesthe read data size. Vector data path side B 116 functional units (L2unit 241, S2 unit 242, M2 unit 243, N2 unit 244, C unit 245 and P unit246) can read from global scalar register file 211 via cross path 117under restrictions that are described below.

FIG. 4 illustrates D1/D2 local register file 214. There are sixteenindependent 64-bit wide scalar registers designated D0 to D16. Eachregister of D1/D2 local register file 214 is read from or written to as64-bits of scalar data. All scalar data path side A 115 functional units(L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225 and D2unit 226) can write to global scalar register file 211. Only D1 unit 225and D2 unit 226 can read from D1/D2 local scalar register file 214. Datastored in D1/D2 local scalar register file 214 can include baseaddresses and offset addresses used in address calculation.

FIG. 5 illustrates L1/S1 local register file 212. In this example, L1/S1local register file 212 includes eight independent 64-bit wide scalarregisters designated AL0 to AL7. In this example, the instruction codingpermits L1/S1 local register file 212 to include up to 16 registers. Inthis example, eight registers are implemented to reduce circuit size andcomplexity. Each register of L1/S1 local register file 212 can be readfrom or written to as 64-bits of scalar data. All scalar data path sideA 115 functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit224, D1 unit 225 and D2 unit 226) can write to L1/S1 local scalarregister file 212. L1 unit 221 and S1 unit 222 can read from L1/S1 localscalar register file 212.

FIG. 6 illustrates M1/N1 local register file 213. In this example, eightindependent 64-bit wide scalar registers designated AM0 to AM7 areimplemented. In this example, the instruction coding permits M1/N1 localregister file 213 to include up to 16 registers. In this example, eightregisters are implemented to reduce circuit size and complexity. Eachregister of M1/N1 local register file 213 can be read from or written toas 64-bits of scalar data. All scalar data path side A 115 functionalunits (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225and D2 unit 226) can write to M1/N1 local scalar register file 213. M1unit 223 and N1 unit 224 can read from M1/N1 local scalar register file213.

FIG. 7 illustrates global vector register file 231. There are sixteenindependent 512-bit wide vector registers. Each register of globalvector register file 231 can be read from or written to as 64-bits ofscalar data designated B0 to B15. Each register of global vectorregister file 231 can be read from or written to as 512-bits of vectordata designated VB0 to VB15. The instruction type determines the datasize. All vector data path side B 116 functional units (L2 unit 241, S2unit 242, M2 unit 243, N2 unit 244, C unit 245 and P unit 246) can reador write to global vector register file 231. Scalar data path side A 115functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1unit 225 and D2 unit 226) can read from global vector register file 231via cross path 117 under restrictions that are described below.

FIG. 8 illustrates predicate (P) local register file 234. There areeight independent 64-bit wide registers designated P0 to P7. Eachregister of P local register file 234 can be read from or written to as64-bits of scalar data. Vector data path side B 116 functional units L2unit 241, S2 unit 242, C unit 244 and P unit 246 can write to P localregister file 234. L2 unit 241, S2 unit 242 and P unit 246 can read fromP local scalar register file 234. One use of P local register file 234is writing one-bit SIMD vector comparison results from L2 unit 241, S2unit 242 or C unit 244, manipulation of the SIMD vector comparisonresults by P unit 246, and use of the manipulated results in control ofa further SIMD vector operation.

FIG. 9 illustrates L2/S2 local register file 232. In this example, eightindependent 512-bit wide vector registers are implemented. In thisexample, the instruction coding permits L2/S2 local register file 232 toinclude up to sixteen registers. In this example, eight registers areimplemented to reduce circuit size and complexity. Each register ofL2/S2 local vector register file 232 can be read from or written to as64-bits of scalar data designated BL0 to BL7. Each register of L2/S2local vector register file 232 can be read from or written to as512-bits of vector data designated VBL0 to VBL7. The instruction typedetermines the data size. All vector data path side B 116 functionalunits (L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 24, C unit 245 andP unit 246) can write to L2/S2 local vector register file 232. L2 unit241 and S2 unit 242 can read from L2/S2 local vector register file 232.

FIG. 10 illustrates M2/N2/C local register file 233. In this example,eight independent 512-bit wide vector registers are implemented. In thisexample, the instruction coding permits M2/N2/C local register file 233to include up to sixteen registers. In this example, eight registers areimplemented to reduce circuit size and complexity. Each register ofM2/N2/C local vector register file 233 can be read from or written to as64-bits of scalar data designated BM0 to BM7. Each register of M2/N2/Clocal vector register file 233 can be read from or written to as512-bits of vector data designated VBM0 to VBM7. All vector data pathside B 116 functional units (L2 unit 241, S2 unit 242, M2 unit 243, N2unit 244, C unit 245 and P unit 246) can write to M2/N2/C local vectorregister file 233. M2 unit 243, N2 unit 244 and C unit 245 can read fromM2/N2/C local vector register file 233.

The provision of global register files accessible by all functionalunits of a side and local register files accessible by some of thefunctional units of a side is a design choice. In another example, adifferent accessibility provision could be made, such as employing onetype of register file corresponding to the global register filesdescribed herein.

Cross path 117 permits limited exchange of data between scalar data pathside A 115 and vector data path side B 116. During each operationalcycle one 64-bit data word can be recalled from global scalar registerfile A 211 for use as an operand by one or more functional units ofvector data path side B 116 and one 64-bit data word can be recalledfrom global vector register file 231 for use as an operand by one ormore functional units of scalar data path side A 115. Any scalar datapath side A 115 functional unit (L1 unit 221, S1 unit 222, M1 unit 223,N1 unit 224, D1 unit 225 and D2 unit 226) can read a 64-bit operand fromglobal vector register file 231. This 64-bit operand is the leastsignificant bits of the 512-bit data in the accessed register of globalvector register file 231. Multiple scalar data path side A 115functional units can employ the same 64-bit cross path data as anoperand during the same operational cycle. However, a single 64-bitoperand is transferred from vector data path side B 116 to scalar datapath side A 115 in a single operational cycle. Any vector data path sideB 116 functional unit (L2 unit 241, S2 unit 242, M2 unit 243, N2 unit244, C unit 245 and P unit 246) can read a 64-bit operand from globalscalar register file 211. If the corresponding instruction is a scalarinstruction, the cross-path operand data is treated as a 64-bit operand.If the corresponding instruction is a vector instruction, the upper 448bits of the operand are zero filled. Multiple vector data path side B116 functional units can employ the same 64-bit cross path data as anoperand during the same operational cycle. In one example, a single64-bit operand is transferred from scalar data path side A 115 to vectordata path side B 116 in a single operational cycle.

Streaming engine 125 (FIG. 1) transfers data in certain restrictedcircumstances. Streaming engine 125 controls two data streams. A streamincludes of a sequence of elements of a particular type. Programs thatoperate on streams read the data sequentially, operating on each elementin turn. Every stream has the following basic properties: the streamdata have a well-defined beginning and ending in time; the stream datahave fixed element size and type throughout the stream; and, the streamdata have a fixed sequence of elements. Once a stream is opened,streaming engine 125 performs the following operations: calculates theaddress; fetches the defined data type from L2 unified cache 130 (whichmay require cache service from a higher level memory, e.g., in the eventof a cache miss in L2); performs data type manipulation such as zeroextension, sign extension, data element sorting/swapping such as matrixtransposition; and delivers the data directly to the programmed dataregister file within processor core 110. Streaming engine 125 is thususeful for real-time digital filtering operations on well-behaved data.Streaming engine 125 frees the corresponding processor from these memoryfetch tasks, thus enabling other processing functions.

Streaming engine 125 provides several benefits. For example, streamingengine 125 permits multi-dimensional memory accesses, increases theavailable bandwidth to the functional units minimizes the number ofcache miss stalls since the stream buffer bypasses L1D cache 123, andreduces the number of scalar operations required to maintain a loop.Streaming engine 125 also manages address pointers and handles addressgeneration which frees up the address generation instruction slots andD1 unit 225 and D2 unit 226 for other computations.

Processor core 110 (FIG. 1) operates on an instruction pipeline.Instructions are fetched in instruction packets of fixed length asfurther described below. All instructions require the same number ofpipeline phases for fetch and decode but require a varying number ofexecute phases.

FIG. 11 illustrates the following pipeline phases: program fetch phase1110, dispatch and decode phases 1120, and execution phases 1130.Program fetch phase 1110 includes three stages for all instructions.Dispatch and decode phases 1120 include three stages for allinstructions. Execution phase 1130 includes one to four stages dependingon the instruction.

Fetch phase 1110 includes program address generation (PG) stage 1111,program access (PA) stage 1112 and program receive (PR) stage 1113.During program address generation stage 1111, the program address isgenerated in the processor and the read request is sent to the memorycontroller for the L1I cache. During the program access stage 1112, theL1I cache processes the request, accesses the data in its memory andsends a fetch packet to the processor boundary. During the programreceive stage 1113, the processor registers the fetch packet.

Instructions are fetched in a fetch packet that includes sixteen 32-bitwide words. FIG. 12 illustrates sixteen instructions 1201 to 1216 of asingle fetch packet. Fetch packets are aligned on 512-bit (16-word)boundaries. This example employs a fixed 32-bit instruction length whichenables decoder alignment. A properly aligned instruction fetch can loadmultiple instructions into parallel instruction decoders. Such aproperly aligned instruction fetch can be achieved by predeterminedinstruction alignment when stored in memory by having fetch packetsaligned on 512-bit boundaries coupled with a fixed instruction packetfetch. Conversely, variable length instructions require an initial stepof locating each instruction boundary before decoding. A fixed lengthinstruction set generally permits more regular layout of instructionfields which simplifies the construction of each decoder which is anadvantage for a wide issue VLIW processor.

The execution of the individual instructions is partially controlled bya p bit in each instruction. In this example, the p bit is bit 0 of the32-bit wide slot. The p bit determines whether an instruction executesin parallel with the next instruction. In this example, instructions arescanned from lower to higher address. If the p bit of an instruction is1, then the next following instruction (higher memory address) isexecuted in parallel with (in the same cycle as) that instruction. Ifthe p bit of an instruction is 0, then the next following instruction isexecuted in the cycle after the instruction.

Processor core 110 (FIG. 1) and L1I cache 121 pipelines (FIG. 1) arede-coupled from each other. Fetch packet returns from L1I cache can takea different number of clock cycles, depending on external circumstancessuch as whether there is a hit in L1I cache 121 or a hit in L2 combinedcache 130. Therefore, program access stage 1112 can take several clockcycles instead of one clock cycle as in the other stages.

The instructions executing in parallel constitute an execute packet. Inthis example, an execute packet can contain up to sixteen 32-bit wideslots for sixteen instructions. No two instructions in an execute packetcan use the same functional unit. A slot is one of five types: 1) aself-contained instruction executed on one of the functional units ofprocessor core 110 (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224,D1 unit 225, D2 unit 226, L2 unit 241, S2 unit 242, M2 unit 243, N2 unit244, C unit 245 and P unit 246); 2) a unitless instruction such as a NOP(no operation) instruction or multiple NOP instructions; 3) a branchinstruction; 4) a constant field extension; and 5) a conditional codeextension. Some of these slot types are further explained herein.

Dispatch and decode phases 1120 (FIG. 11) include instruction dispatchto appropriate execution unit (DS) stage 1121, instruction pre-decode(DC1) stage 1122, and instruction decode, operand read (DC2) stage 1123.During instruction dispatch to appropriate execution unit stage 1121,the fetch packets are split into execute packets and assigned to theappropriate functional units. During the instruction pre-decode stage1122, the source registers, destination registers, and associated pathsare decoded for the execution of the instructions in the functionalunits. During the instruction decode, operand read stage 1123, moredetailed unit decodes are performed and operands are read from theregister files.

Execution phase 1130 includes execution (E1 to E5) stages 1131 to 1135.Different types of instructions require different numbers of such stagesto complete execution. The execution stages of the pipeline play animportant role in understanding the device state at processor cycleboundaries.

During E1 stage 1131, the conditions for the instructions are evaluatedand operands are operated on. As illustrated in FIG. 11, E1 stage 1131can receive operands from a stream buffer 1141 and one of the registerfiles shown schematically as 1142. For load and store instructions,address generation is performed, and address modifications are writtento a register file. For branch instructions, the branch fetch packet inPG phase is affected. As illustrated in FIG. 11, load and storeinstructions access memory here shown schematically as memory 1151. Forsingle-cycle instructions, results are written to a destination registerfile when any conditions for the instructions are evaluated as true. Ifa condition is evaluated as false, the instruction does not write anyresults or have any pipeline operation after E1 stage 1131.

During E2 stage 1132, load instructions send the address to memory.Store instructions send the address and data to memory. Single-cycleinstructions that saturate results set the SAT bit in the control statusregister (CSR) if saturation occurs. For 2-cycle instructions, resultsare written to a destination register file.

During E3 stage 1133, data memory accesses are performed. Any multiplyinstructions that saturate results set the SAT bit in the control statusregister (CSR) if saturation occurs. For 3-cycle instructions, resultsare written to a destination register file.

During E4 stage 1134, load instructions bring data to the processorboundary. For 4-cycle instructions, results are written to a destinationregister file.

During E5 stage 1135, load instructions write data into a register asillustrated schematically in FIG. 11 with input from memory 1151 to E5stage 1135.

FIG. 13 illustrates an example of the instruction coding 1300 offunctional unit instructions used by this example. Each instructionincludes 32 bits and controls the operation of one of the individuallycontrollable functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1unit 224, D1 unit 225, D2 unit 226, L2 unit 241, S2 unit 242, M2 unit243, N2 unit 244, C unit 245 and P unit 246).

The creg field 1301 (bits 29 to 31) and the z bit 1302 (bit 28) areoptional fields used in conditional instructions. The bits are used forconditional instructions to identify the predicate register and thecondition. The z bit 1302 (bit 28) indicates whether the predication isbased upon zero or not zero in the predicate register. If z=1, the testis for equality with zero. If z=0, the test is for nonzero. The case ofcreg=0 and z=0 is treated as true to allow unconditional instructionexecution. The creg field 1301 and the z field 1302 are encoded in theinstruction as shown in Table 1.

TABLE 1 Conditional creg z Register 31 30 29 28 Unconditional 0 0 0 0Reserved 0 0 0 1 A0 0 0 1 z A1 0 1 0 z A2 0 1 1 z A3 1 0 0 z A4 1 0 1 zA5 1 1 0 z Reserved 1 1 x x

Execution of a conditional instruction is conditional upon the valuestored in the specified data register. The data register is in theglobal scalar register file 211 for all functional units. Note that “z”in the z bit column refers to the zero/not zero comparison selectionnoted above and “x” is a don't care state. This coding specifies asubset of the sixteen global registers as predicate registers whichpreserves bits in the instruction coding. Note that unconditionalinstructions do not have the optional bits. For unconditionalinstructions, the bits in fields 1301 and 1302 (28 to 31) are used asadditional opcode bits.

The dst field 1303 (bits 23 to 27) specifies a register in acorresponding register file as the destination of the instructionresults.

The src2/cst field 1304 (bits 18 to 22) has several meanings dependingon the instruction opcode field (bits 3 to 12 for all instructions andadditionally bits 28 to 31 for unconditional instructions). One meaningspecifies a register of a corresponding register file as the secondoperand. Another meaning is an immediate constant. Depending on theinstruction type, the field 1304 is treated as an unsigned integer andzero extended to a specified data length or is treated as a signedinteger and sign extended to the specified data length.

The src1 field 1305 (bits 13 to 17) specifies a register in acorresponding register file as the first source operand.

The opcode field 1306 (bits 3 to 12) for all instructions (andadditionally bits 28 to 31 for unconditional instructions) specifies thetype of instruction and designates appropriate instruction optionsincluding unambiguous designation of the functional unit used andoperation performed. A detailed explanation of the opcode is beyond thescope of this description except for the instruction options describedbelow.

The e bit 1307 (bit 2) is used for immediate constant instructions wherethe constant can be extended. If e=1, then the immediate constant isextended in a manner described below. If e=0, then the immediateconstant is not extended and the immediate constant is specified by thesrc2/cst field 1304 (bits 18 to 22). Note that the e bit 1307 is usedfor some instructions. Accordingly, with proper coding, the e bit 1307can be omitted from some instructions and the bit can be used as anadditional opcode bit.

The s bit 1308 (bit 1) designates scalar data path side A 115 or vectordata path side B 116. If s=0, then scalar data path side A 115 isselected which limits the functional unit to L1 unit 221, S1 unit 222,M1 unit 223, N1 unit 224, D1 unit 225 and D2 unit 226 and thecorresponding register files illustrated in FIG. 2. Similarly, s=1selects vector data path side B 116 which limits the functional unit toL2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244, P unit 246 and thecorresponding register file illustrated in FIG. 2.

The p bit 1309 (bit 0) marks the execute packets. The p-bit determineswhether the instruction executes in parallel with the followinginstruction. The p-bits are scanned from lower to higher address. If p=1for the current instruction, then the next instruction executes inparallel with the current instruction. If p=0 for the currentinstruction, then the next instruction executes in the cycle after thecurrent instruction. All instructions executing in parallel constitutean execute packet. An execute packet can contain up to sixteeninstructions. Each instruction in an execute packet uses a differentfunctional unit.

There are two different condition code extension slots. Each executepacket can contain one each of these unique 32-bit condition codeextension slots which contains the 4-bit creg/z fields for theinstructions in the same execute packet. FIG. 14 illustrates the codingfor condition code extension slot 0 and FIG. 15 illustrates the codingfor condition code extension slot 1.

FIG. 14 illustrates the coding for condition code extension slot 0having 32 bits. Field 1401 (bits 28 to 31) specifies 4 creg/z bitsassigned to the L1 unit 221 instruction in the same execute packet.Field 1402 (bits 27 to 24) specifies four creg/z bits assigned to the L2unit 241 instruction in the same execute packet. Field 1403 (bits 20 to23) specifies four creg/z bits assigned to the S1 unit 222 instructionin the same execute packet. Field 1404 (bits 16 to 19) specifies fourcreg/z bits assigned to the S2 unit 242 instruction in the same executepacket. Field 1405 (bits 12 to 15) specifies four creg/z bits assignedto the D1 unit 225 instruction in the same execute packet. Field 1406(bits 8 to 11) specifies four creg/z bits assigned to the D2 unit 226instruction in the same execute packet. Field 1407 (bits 6 and 7) isunused/reserved. Field 1408 (bits 0 to 5) is coded as a set of uniquebits (CCEX0) to identify the condition code extension slot 0. Once theunique ID of condition code extension slot 0 is detected, thecorresponding creg/z bits are employed to control conditional executionof any L1 unit 221, L2 unit 241, S1 unit 222, S2 unit 242, D1 unit 225and D2 unit 226 instruction in the same execution packet. The creg/zbits are interpreted as shown in Table 1. If the correspondinginstruction is conditional (includes creg/z bits), the correspondingbits in the condition code extension slot 0 override the condition codebits in the instruction. Setting the creg/z bits equal to “0000” makesthe instruction unconditional. Thus, a properly coded condition codeextension slot 0 can make some corresponding instructions conditionaland some unconditional.

FIG. 15 illustrates the coding for condition code extension slot 1having 32 bits. Field 1501 (bits 28 to 31) specifies four creg/z bitsassigned to the M1 unit 223 instruction in the same execute packet.Field 1502 (bits 27 to 24) specifies four creg/z bits assigned to the M2unit 243 instruction in the same execute packet. Field 1503 (bits 19 to23) specifies four creg/z bits assigned to the C unit 245 instruction inthe same execute packet. Field 1504 (bits 16 to 19) specifies fourcreg/z bits assigned to the N1 unit 224 instruction in the same executepacket. Field 1505 (bits 12 to 15) specifies four creg/z bits assignedto the N2 unit 244 instruction in the same execute packet. Field 1506(bits 6 to 11) is unused/reserved. Field 1507 (bits 0 to 5) is coded asa set of unique bits (CCEX1) to identify the condition code extensionslot 1. Once the unique ID of condition code extension slot 1 isdetected, the corresponding creg/z bits are employed to controlconditional execution of any M1 unit 223, M2 unit 243, C unit 245, N1unit 224 and N2 unit 244 instruction in the same execution packet. Thesecreg/z bits are interpreted as shown in Table 1. If the correspondinginstruction is conditional (includes creg/z bits), the correspondingbits in the condition code extension slot 1 override the condition codebits in the instruction. Setting the creg/z bits equal to “0000” makesthe instruction unconditional. Thus, a properly coded condition codeextension slot 1 can make some instructions conditional and someunconditional.

Both condition code extension slot 0 and condition code extension slot 1can include a p bit to define an execute packet as described above inconjunction with FIG. 13. In this example, as illustrated in FIGS. 14and 15, code extension slot 0 and condition code extension slot 1 havebit 0 (p bit) encoded as 1. Thus, neither condition code extension slot0 nor condition code extension slot 1 can be in the last instructionslot of an execute packet.

There are two different 32-bit constant extension slots. Each executepacket can contain one each of the unique constant extension slots whichcontains 27 bits to be concatenated as high order bits with the 5-bitconstant field 1305 to form a 32-bit constant. As noted in theinstruction coding description above, some instructions define thesrc2/cst field 1304 as a constant rather than a source registeridentifier. At least some of such instructions can employ a constantextension slot to extend the constant to 32 bits.

FIG. 16 illustrates the fields of constant extension slot 0. Eachexecute packet can include one instance of constant extension slot 0 andone instance of constant extension slot 1. FIG. 16 illustrates thatconstant extension slot 0 1600 includes two fields. Field 1601 (bits 5to 31) constitutes the most significant 27 bits of an extended 32-bitconstant including the target instruction scr2/cst field 1304 as thefive least significant bits. Field 1602 (bits 0 to 4) is coded as a setof unique bits (CSTX0) to identify the constant extension slot 0. Inthis example, constant extension slot 0 1600 can be used to extend theconstant of one of an L1 unit 221 instruction, data in a D1 unit 225instruction, an S2 unit 242 instruction, an offset in a D2 unit 226instruction, an M2 unit 243 instruction, an N2 unit 244 instruction, abranch instruction, or a C unit 245 instruction in the same executepacket. Constant extension slot 1 is similar to constant extension slot0 except that bits 0 to 4 are coded as a set of unique bits (CSTX1) toidentify the constant extension slot 1. In this example, constantextension slot 1 can be used to extend the constant of one of an L2 unit241 instruction, data in a D2 unit 226 instruction, an S1 unit 222instruction, an offset in a D1 unit 225 instruction, an M1 unit 223instruction or an N1 unit 224 instruction in the same execute packet.

Constant extension slot 0 and constant extension slot 1 are used asfollows. The target instruction is of the type permitting constantspecification. In this example, the extension is implemented byreplacing one input operand register specification field with the leastsignificant bits of the constant as described above with respect toscr2/cst field 1304. Instruction decoder 113 determines this case, knownas an immediate field, from the instruction opcode bits. The targetinstruction also includes one constant extension bit (e bit 1307)dedicated to signaling whether the specified constant is not extended(constant extension bit=0) or extended (constant extension bit=1). Ifinstruction decoder 113 detects a constant extension slot 0 or aconstant extension slot 1, instruction decoder 113 further checks theother instructions within the execute packet for an instructioncorresponding to the detected constant extension slot. A constantextension is made if one corresponding instruction has a constantextension bit (e bit 1307) equal to 1.

FIG. 17 is a partial block diagram 1700 illustrating constant extension.FIG. 17 assumes that instruction decoder 113 (FIG. 1) detects a constantextension slot and a corresponding instruction in the same executepacket. Instruction decoder 113 supplies the twenty-seven extension bitsfrom the constant extension slot (bit field 1601) and the five constantbits (bit field 1305) from the corresponding instruction to concatenator1701. Concatenator 1701 forms a single 32-bit word from these two parts.In this example, the twenty-seven extension bits from the constantextension slot (bit field 1601) are the most significant bits and thefive constant bits (bit field 1305) are the least significant bits. Thecombined 32-bit word is supplied to one input of multiplexer 1702. Thefive constant bits from the corresponding instruction field 1305 supplya second input to multiplexer 1702. Selection of multiplexer 1702 iscontrolled by the status of the constant extension bit. If the constantextension bit (e bit 1307) is 1 (extended), multiplexer 1702 selects theconcatenated 32-bit input. If the constant extension bit is 0 (notextended), multiplexer 1702 selects the five constant bits from thecorresponding instruction field 1305. The output of multiplexer 1702supplies an input of sign extension unit 1703.

Sign extension unit 1703 forms the final operand value from the inputfrom multiplexer 1703. Sign extension unit 1703 receives control inputsScalar/Vector and Data Size. The Scalar/Vector input indicates whetherthe corresponding instruction is a scalar instruction or a vectorinstruction. The functional units of data path side A 115 (L1 unit 221,S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225 and D2 unit 226)perform scalar instructions. Any instruction directed to one of thesefunctional units is a scalar instruction. Data path side B functionalunits L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244 and C unit 245can perform scalar instructions or vector instructions. Instructiondecoder 113 determines whether the instruction is a scalar instructionor a vector instruction from the opcode bits. P unit 246 may performsscalar instructions. The Data Size can be eight bits (byte B), sixteenbits (half-word H), 32 bits (word W), or 64 bits (double word D).

Table 2 lists the operation of sign extension unit 1703 for the variousoptions.

TABLE 2 Instruction Operand Constant Type Size Length Action ScalarB/H/W/D  5 bits Sign extend to 64 bits Scalar B/H/W/D 32 bits Signextend to 64 bits Vector B/H/W/D  5 bits Sign extend to operand size andreplicate across whole vector Vector B/H/W 32 bits Replicate 32-bitconstant across each 32-bit (W) lane Vector D 32 bits Sign extend to 64bits and replicate across each 64-bit (D) lane

Both constant extension slot 0 and constant extension slot 1 can includea p bit to define an execute packet as described above in conjunctionwith FIG. 13. In this example, as in the case of the condition codeextension slots, constant extension slot 0 and constant extension slot 1have bit 0 (p bit) encoded as 1. Thus, neither constant extension slot 0nor constant extension slot 1 can be in the last instruction slot of anexecute packet.

An execute packet can include a constant extension slot 0 or 1 and morethan one corresponding instruction marked constant extended (e bit=1).For such an occurrence, for constant extension slot 0, more than one ofan L1 unit 221 instruction, data in a D1 unit 225 instruction, an S2unit 242 instruction, an offset in a D2 unit 226 instruction, an M2 unit243 instruction or an N2 unit 244 instruction in an execute packet canhave an e bit of 1. For such an occurrence, for constant extension slot1, more than one of an L2 unit 241 instruction, data in a D2 unit 226instruction, an S1 unit 222 instruction, an offset in a D1 unit 225instruction, an M1 unit 223 instruction or an N1 unit 224 instruction inan execute packet can have an e bit of 1. In one example, instructiondecoder 113 determines that such an occurrence is an invalid operationand not supported. Alternately, the combination can be supported withextension bits of the constant extension slot applied to eachcorresponding functional unit instruction marked constant extended.

L1 unit 221, S1 unit 222, L2 unit 241, S2 unit 242 and C unit 245 oftenoperate in a single instruction multiple data (SIMD) mode. In this SIMDmode, the same instruction is applied to packed data from the twooperands. Each operand holds multiple data elements disposed inpredetermined slots. SIMD operation is enabled by carry control at thedata boundaries. Such carry control enables operations on varying datawidths.

FIG. 18 illustrates the carry control logic. AND gate 1801 receives thecarry output of bit N within the operand wide arithmetic logic unit (64bits for scalar data path side A 115 functional units and 512 bits forvector data path side B 116 functional units). AND gate 1801 alsoreceives a carry control signal which is further explained below. Theoutput of AND gate 1801 is supplied to the carry input of bit N+1 of theoperand wide arithmetic logic unit. AND gates such as AND gate 1801 aredisposed between every pair of bits at a possible data boundary. Forexample, for 8-bit data such an AND gate will be between bits 7 and 8,bits 15 and 16, bits 23 and 24, etc. Each such AND gate receives acorresponding carry control signal. If the data size is the minimumsize, each carry control signal is 0, effectively blocking carrytransmission between the adjacent bits. The corresponding carry controlsignal is 1 if the selected data size requires both arithmetic logicunit sections. Table 3 below shows example carry control signals for thecase of a 512-bit wide operand as used by vector data path side B 116functional units which can be divided into sections of 8 bits, 16 bits,32 bits, 64 bits, 128 bits or 256 bits. In Table 3, the upper 32 bitscontrol the upper bits (bits 128 to 511) carries and the lower 32 bitscontrol the lower bits (bits 0 to 127) carries. No control of the carryoutput of the most significant bit is needed, thus only 63 carry controlsignals are required.

TABLE 3 Data Size Carry Control Signals  8 bits (B) -000 0000 0000 00000000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000  16 bits (H)-101 0101 0101 0101 0101 0101 0101 0101 0101 0101 0101 0101 0101 01010101 0101  32 bits (W) -111 0111 0111 0111 0111 0111 0111 0111 0111 01110111 0111 0111 0111 0111 0111  64 bits (D) -111 1111 0111 1111 0111 11110111 1111 0111 1111 0111 1111 0111 1111 0111 1111 128 bits -111 11111111 1111 0111 1111 1111 1111 0111 1111 1111 1111 0111 1111 1111 1111256 bits -111 1111 1111 1111 1111 1111 1111 1111 0111 1111 1111 11111111 1111 1111 1111

Operation on data sizes that are integral powers of 2 (2^(N)) is common.However, the carry control technique is not limited to integral powersof 2 and can be applied to other data sizes and operand widths.

In this example, at least L unit 241 and S unit 242 employ two types ofSIMD instructions using registers in predicate register file 234. Inthis example, the SIMD vector predicate instructions operate on aninstruction specified data size. The data sizes include byte (8 bit)data, half word (16 bit) data, word (32 bit) data, double word (64 bit)data, quad word (128 bit) data and half vector (256 bit) data. In thefirst of these instruction types, the functional unit (L unit 241 or Sunit 242) performs a SIMD comparison on packed data in two general dataregisters and supplies results to a predicate data register. Theinstruction specifies a data size, the two general data registeroperands, and the destination predicate register. In this example, eachpredicate data register includes one bit corresponding to each minimaldata size portion of the general data registers. In the current example,the general data registers are 512 bits (64 bytes) and the predicatedata registers are 64 bits (8 bytes). Each bit of a predicate dataregister corresponds to eight bits of a general data register. Thecomparison is performed on a specified data size (8, 16, 32, 64, 128 or256 bits). If the comparison is true, then the functional unit suppliesl's to all predicate register bits corresponding the that data sizeportion. If the comparison is false, the functional unit supplies zeroesto the predicate register bits corresponding to that data size portion.In this example, the enabled comparison operations include: less than,greater than, and equal to.

In the second of the instruction types, the functional unit (L unit 241or S unit 242) separately performs a first SIMD operation or a secondSIMD operation on packed data in general data registers based upon thestate of data in a predicate data register. The instruction specifies adata size, one or two general data register operands, a controllingpredicate register, and a general data register destination. Forexample, a functional unit can select, for each data sized portion oftwo vector operands, a first data element of a first operand or a seconddata element of a second operand dependent upon the 1/0 state ofcorresponding bits in the predicate data register to store in thedestination register. In another example, the data elements of a singlevector operand can be saved to memory or not saved dependent upon thedata of the corresponding bits of the predicate register.

The operations of P unit 245 permit a variety of compound vector SIMDoperations based upon more than one vector comparison. For example, arange determination can be made using two comparisons. In a SIMDoperation, a candidate vector is compared with a vector reference havingthe minimum of the range packed within a data register. The greater thanresult is scalar data with bits corresponding to the SIMD data width setto 0 or 1 depending upon the SIMD comparison and is stored in apredicate data register. Another SIMD comparison of the candidate vectoris performed with another reference vector having the maximum of therange packed within a different data register produces another scalarwith less than results stored in another predicate register. The P unitthen ANDs the two predicate registers. The AND result indicates whethereach SIMD data part of the candidate vector is within range or out ofrange. A P unit BITCNT instruction of the AND result can produce a countof the data elements within the comparison range. The P unit NEGfunction can be used to convert: a less than comparison result to agreater than or equal comparison result; a greater than comparisonresult to a less than or equal to comparison result; or, an equal tocomparison result to a not equal to comparison result.

Streaming Engine

FIG. 19 is a conceptual view of the streaming engine 125 of the exampleprocessor 100 of FIG. 1. FIG. 19 illustrates the processing of a singlestream representative of the two streams controlled by streaming engine125. Streaming engine 1900 includes stream address generator 1901.Stream address generator 1901 sequentially generates addresses of theelements of the stream and supplies these element addresses to systemmemory 1910. Memory 1910 recalls data stored at the element addresses(data elements) and supplies these data elements to datafirst-in-first-out (FIFO) buffer 1902. Data FIFO buffer 1902 providesbuffering between memory 1910 and processor 1920. Data formatter 1903receives the data elements from data FIFO memory 1902 and provides dataformatting according to the stream definition. This process is describedin more detail herein. Streaming engine 1900 supplies the formatted dataelements from data formatter 1903 to the processor 1920. A programexecuting on processor 1920 consumes the data and generates an output.

Stream elements typically reside in system memory. The memory imposes noparticular structure upon the stream. Programs define streams andthereby impose structure by specifying the stream attributes such asaddress of the first element of the stream, size and type of theelements in the stream, formatting for data in the stream, and theaddress sequence associated with the stream.

The streaming engine defines an address sequence for elements of thestream in terms of a pointer walking through memory. A multiple-levelnested loop controls the path the pointer takes. An iteration count fora loop level indicates the number of times the level repeats. Adimension gives the distance between pointer positions of the looplevel.

In a basic forward stream, the innermost loop consumes physicallycontiguous elements from memory as the implicit dimension of theinnermost loop is one element. The pointer moves from element to elementin consecutive, increasing order. In each level outside the inner loop,that loop moves the pointer to a new location based on the size of thedimension of the loop level.

This form of addressing allows programs to specify regular paths throughmemory using a small number of parameters. Table 4 lists the addressingparameters of a basic stream.

TABLE 4 Parameter Definition ELEM_BYTES Size of each element in bytesICNT0 Number of iterations for the innermost loop level 0. At loop level0 all elements are physically contiguous. Implied DIM0 = ELEM_BYTESICNT1 Number of iterations for loop level 1 DIM1 Number of bytes betweenthe starting points for consecutive iterations of loop level 1 ICNT2Number of iterations for loop level 2 DIM2 Number of bytes between thestarting points for consecutive iterations of loop level 2 ICNT3 Numberof iterations for loop level 3 DIM3 Number of bytes between the startingpoints for consecutive iterations of loop level 3 ICNT4 Number ofiterations for loop level 4 DIM4 Number of bytes between the startingpoints for consecutive iterations of loop level 4 ICNT5 Number ofiterations for loop level 5 DIM5 Number of bytes between the startingpoints for consecutive iterations of loop level 5

In this example, ELEM_BYTES ranges from 1 to 64 bytes as shown in Table5.

TABLE 5 ELEM_BYTES Stream Element Length 000 1 byte  001 2 bytes 010 4bytes 011 8 bytes 100 16 bytes  101 32 bytes  110 64 bytes  111 Reserved

The definition above maps consecutive elements of the stream toincreasing addresses in memory which is appropriate for many algorithms.Some algorithms are better served by reading elements in decreasingmemory address order or reverse stream addressing. For example, adiscrete convolution computes vector dot-products, as illustrated byexpression (1).

(f*g)[t]=Σ_(x=−∞) ^(∞) f[x]g[t−x]  (1)

In expression (1), f[ ] and g[ ] represent arrays in memory. For eachoutput, the algorithm reads f[ ] in the forward direction and reads g[ ]in the reverse direction. Practical filters limit the range of indicesfor [x] and [t−x] to a finite number of elements. To support thispattern, the streaming engine supports reading elements in decreasingaddress order.

Matrix multiplication presents a unique problem to the streaming engine.Each element in the matrix product is a vector dot product between a rowfrom the first matrix and a column from the second. Programs typicallystore matrices in row-major or column-major order. Row-major orderstores all the elements of a single row contiguously in memory.Column-major order stores all elements of a single column contiguouslyin memory. Matrices are typically stored in the same order as thedefault array order for the language. As a result, only one of the twomatrices in a matrix multiplication map on to the 2-dimensional streamdefinition of the streaming engine. In a typical example, an index stepsthrough columns on one array and rows of the other array. The streamingengine supports implicit matrix transposition with transposed streams.Transposed streams avoid the cost of explicitly transforming the data inmemory. Instead of accessing data in strictly consecutive-element order,the streaming engine effectively interchanges the inner two loopdimensions of the traversal order, fetching elements along the seconddimension into contiguous vector lanes.

This algorithm works but is impractical to implement for small elementsizes. Some algorithms work on matrix tiles which are multiple columnsand rows together. Therefore, the streaming engine defines a separatetransposition granularity. The hardware imposes a minimum granularity.The transpose granularity needs to be at least as large as the elementsize. Transposition granularity causes the streaming engine to fetch oneor more consecutive elements from dimension 0 before moving alongdimension 1. When the granularity equals the element size, a singlecolumn from a row-major array is fetched. Otherwise, the granularityspecifies fetching two, four or more columns at a time from a row-majorarray. This is also applicable for column-major layout by exchanging rowand column in the description. A parameter GRANULE indicates thetransposition granularity in bytes.

Another common matrix multiplication technique exchanges the innermosttwo loops of the matrix multiply. The resulting inner loop no longerreads down the column of one matrix while reading across the row ofanother. For example, the algorithm may hoist one term outside the innerloop, replacing it with the scalar value. The innermost loop can beimplemented with a single scalar by vector multiply followed by a vectoradd. Or, the scalar value can be duplicated across the length of thevector and a vector by vector multiply used. The streaming engine ofthis example directly supports the latter case and related use modelswith an element duplication mode. In this mode, the streaming enginereads a granule smaller than the full vector size and replicates thatgranule to fill the next vector output.

The streaming engine treats each complex number as a single element withtwo sub-elements that give the real and imaginary (rectangular) ormagnitude and angle (polar) portions of the complex number. Not allprograms or peripherals agree what order these sub-elements shouldappear in memory. Therefore, the streaming engine offers the ability toswap the two sub-elements of a complex number with no cost. The featureswaps the halves of an element without interpreting the contents of theelement and can be used to swap pairs of sub-elements of any type, notjust complex numbers.

Algorithms generally prefer to work at high precision, but highprecision values require more storage and bandwidth than lower precisionvalues. Commonly, programs store data in memory at low precision,promote those values to a higher precision for calculation, and thendemote the values to lower precision for storage. The streaming enginesupports such operations directly by allowing algorithms to specify onelevel of type promotion. In this example, every sub-element can bepromoted to a larger type size with either sign or zero extension forinteger types. In some examples, the streaming engine supports floatingpoint promotion, promoting 16-bit and 32-bit floating point values to32-bit and 64-bit formats, respectively.

While the streaming engine defines a stream as a discrete sequence ofdata elements, the processing unit core 110 consumes data elementspacked contiguously in vectors. The vectors resemble streams as thevectors contain multiple homogeneous elements with some implicitsequence. Because the streaming engine reads streams, but the processingunit core 110 consumes vectors, the streaming engine maps streams ontovectors in a consistent way.

Vectors include equal-sized lanes, each lane containing a sub-element.The processing unit core 110 designates the rightmost lane of the vectoras lane 0, regardless of current endian mode. Lane numbers increaseright-to-left. The actual number of lanes within a vector variesdepending on the length of the vector and the data size of thesub-element.

FIG. 20 illustrates the sequence of the formatting operations offormatter 1903. Formatter 1903 includes three sections: input section2010, formatting section 2020, and output section 2030. Input section2010 receives the data recalled from system memory 1910 as accessed bystream address generator 1901. The data can be via linear fetch stream2011 or transposed fetch stream 2012.

Formatting section 2020 includes various formatting blocks. Theformatting performed within formatter 1903 by the blocks is furtherdescribed below. Complex swap block 2021 optionally swaps twosub-elements forming a complex number element. Type promotion block 2022optionally promotes each data element into a larger data size. Promotionincludes zero extension for unsigned integers and sign extension forsigned integers. Decimation block 2023 optionally decimates the dataelements. In this example, decimation can be 2:1 retaining every otherdata element or 4:1 retaining every fourth data element. Elementduplication block 2024 optionally duplicates individual data elements.In this example, the data element duplication is an integer power of 2(2N, where N is an integer) including 2×, 4×, 8×, 16×, 32× and 64×. Inthis example, data duplication can extend over multiple destinationvectors. Vector length masking/group duplication block 2025 has twoprimary functions. An independently specified vector length VECLENcontrols the data elements supplied to each output data vector. Whengroup duplication is off, excess lanes in the output data vector arezero filled and these lanes are marked invalid. When group duplicationis on, input data elements of the specified vector length are duplicatedto fill the output data vector.

Output section 2030 holds the data for output to the correspondingfunctional units. Register and buffer for processor 2031 stores aformatted vector of data to be used as an operand by the functionalunits of processing unit core 110 (FIG. 1).

FIG. 21 illustrates an example of lane allocation in a vector. Vector2100 is divided into eight 64-bit lanes (8×64 bits=512 bits, the vectorlength). Lane 0 includes bits 0 to 63, line 1 includes bits 64 to 127,lane 2 includes bits 128 to 191, lane 3 includes bits 192 to 255, lane 4includes bits 256 to 319, lane 5 includes bits 320 to 383, lane 6includes bits 384 to 447. and lane 7 includes bits 448 to 511.

FIG. 22 illustrates another example of lane allocation in a vector.Vector 2210 is divided into sixteen 32-bit lanes (16×32 bits=512 bits,the vector length). Lane 0 includes bits 0 to 31, line 1 includes bits32 to 63, lane 2 includes bits 64 to 95, lane 3 includes bits 96 to 127,lane 4 includes bits 128 to 159, lane 5 includes bits 160 to 191, lane 6includes bits 192 to 223, lane 7 includes bits 224 to 255, lane 8includes bits 256 to 287, lane 9 includes bits 288 to 319, lane 10includes bits 320 to 351, lane 11 includes bits 352 to 383, lane 12includes bits 384 to 415, lane 13 includes bits 416 to 447, lane 14includes bits 448 to 479, and lane 15 includes bits 480 to 511.

The streaming engine maps the innermost stream dimension directly tovector lanes. The streaming engine maps earlier elements within theinnermost stream dimension to lower lane numbers and later elements tohigher lane numbers, regardless of whether the stream advances inincreasing or decreasing address order. Whatever order the streamdefines, the streaming engine deposits elements in vectors inincreasing-lane order. For non-complex data, the streaming engine placesthe first element in lane 0 of the vector processing unit core 110(FIG. 1) fetches, the second in lane 1, and so on. For complex data, thestreaming engine places the first element in lanes 0 and 1, the secondelement in lanes 2 and 3, and so on. Sub-elements within an elementretain the same relative ordering regardless of the stream direction.For non-swapped complex elements, the sub-elements with the loweraddress of each pair are placed in the even numbered lanes, and thesub-elements with the higher address of each pair are placed in the oddnumbered lanes. For swapped complex elements, the placement is reversed.

The streaming engine fills each vector processing unit core 110 fetcheswith as many elements as possible from the innermost stream dimension.If the innermost dimension is not a multiple of the vector length, thestreaming engine zero pads the dimension to a multiple of the vectorlength. As noted below, the streaming engine also marks the lanesinvalid. Thus, for higher-dimension streams, the first element from eachiteration of an outer dimension arrives in lane 0 of a vector. Thestreaming engine maps the innermost dimension to consecutive lanes in avector. For transposed streams, the innermost dimension includes groupsof sub-elements along dimension 1, not dimension 0, as transpositionexchanges these two dimensions.

Two-dimensional (2D) streams exhibit greater variety as compared toone-dimensional streams. A basic 2D stream extracts a smaller rectanglefrom a larger rectangle. A transposed 2D stream reads a rectanglecolumn-wise instead of row-wise. A looping stream, where the seconddimension overlaps first, executes a finite impulse response (FIR)filter taps which loops repeatedly over FIR filter samples providing asliding window of input samples.

FIG. 23 illustrates a region of memory that can be accessed using abasic two-dimensional stream. The inner two dimensions, represented byELEM_BYTES, ICNT0, DIM1 and ICNT1 (refer to Table 4), give sufficientflexibility to describe extracting a smaller rectangle 2320 havingdimensions 2321 and 2322 from a larger rectangle 2310 having dimensions2311 and 2312. In this example, rectangle 2320 is a 9 by 13 rectangle of64-bit values and rectangle 2310 is a larger 11 by 19 rectangle. Thefollowing stream parameters define this stream: ICNT0=9, ELEM_BYTES=8,ICNT1=13, and DIM1=88 (11 times 8).

Thus, the iteration count in the 0-dimension 2321 is nine and theiteration count in the 1-dimension 2322 is thirteen. Note that theELEM_BYTES scales the innermost dimension. The first dimension has ICNT0elements of size ELEM_BYTES. The stream address generator does not scalethe outer dimensions. Therefore, DIM1=88, which is eleven elementsscaled by eight bytes per element.

FIG. 24 illustrates the order of elements within the example stream ofFIG. 23. The streaming engine fetches elements for the stream in theorder illustrated in order 2400. The first nine elements come from thefirst row of rectangle 2320, left-to-right in hops 1 to 8. The 10ththrough 24th elements comes from the second row, and so on. When thestream moves from the 9th element to the 10th element (hop 9 in FIG.24), the streaming engine computes the new location based on theposition of the pointer at the start of the inner loop, not the positionof the pointer at the end of the first dimension. Thus, DIM1 isindependent of ELEM_BYTES and ICNT0. DIM1 represents the distancebetween the first bytes of each consecutive row.

Transposed streams are accessed along dimension 1 before dimension 0.The following examples illustrate transposed streams with varyingtransposition granularity. FIG. 25 illustrates extracting a smallerrectangle 2520 (12×8) having dimensions 2521 and 2522 from a largerrectangle 2510 (14×13) having dimensions 2511 and 2512. In FIG. 25,ELEM_BYTES equal 2.

FIG. 26 illustrates how the streaming engine fetches the stream of theexample stream of FIG. 25 with a transposition granularity of fourbytes. Fetch pattern 2600 fetches pairs of elements from each row(because the granularity of four is twice the ELEM_BYTES of two), butotherwise moves down the columns. Once the streaming engine reaches thebottom of a pair of columns, the streaming engine repeats the patternwith the next pair of columns.

FIG. 27 illustrates how the streaming engine fetches the stream of theexample stream of FIG. 25 with a transposition granularity of eightbytes. The overall structure remains the same. The streaming enginefetches four elements from each row (because the granularity of eight isfour times the ELEM_BYTES of two) before moving to the next row in thecolumn as shown in fetch pattern 2700.

The streams examined so far read each element from memory exactly once.A stream can read a given element from memory multiple times, in effectlooping over a portion of memory. FIR filters exhibit two common loopingpatterns: re-reading the same filter taps for each output and readinginput samples from a sliding window. Two consecutive outputs need inputsfrom two overlapping windows.

FIG. 28 illustrates the details of streaming engine 125 of FIG. 1.Streaming engine 125 contains three major sections: Stream 0 2810;Stream 1 2820; and Shared L2 Interfaces 2830. Stream 0 2810 and Stream 12820 both contain identical hardware that operates in parallel. Stream 02810 and Stream 1 2820 both share L2 interfaces 2830. Each stream 2810and 2820 provides processing unit core 110 (FIG. 1) data at a rate of upto 512 bits/cycle, every cycle, which is enabled by the dedicated streampaths and shared dual L2 interfaces.

Each streaming engine 125 includes a respective dedicated 6-dimensional(6D) stream address generator 2811/2821 that can each generate one newnon-aligned request per cycle. As is further described herein, addressgenerators 2811/2821 output 512-bit aligned addresses that overlap theelements in the sequence defined by the stream parameters.

Each address generator 2811/2821 connects to a respective dedicatedmicro table look-aside buffer (μTLB) 2812/2822. The μTLB 2812/2822converts a single 48-bit virtual address to a 44-bit physical addresseach cycle. Each μTLB 2812/2822 has 8 entries, covering a minimum of 32kB with 4 kB pages or a maximum of 16 MB with 2 MB pages. Each addressgenerator 2811/2821 generates 2 addresses per cycle. The μTLB 2812/2822only translates one address per cycle. To maintain throughput, streamingengine 125 operates under the assumption that most stream references arewithin the same 4 kB page. Thus, the address translation does not modifybits 0 to 11 of the address. If aout0 and aout1 line in the same 4 kBpage (aout0[47:12] are the same aout1[47:12]), then the μTLB 2812/2822only translates aout0 and reuses the translation for the upper bits ofboth addresses.

Translated addresses are queued in respective command queue 2813/2823.These addresses are aligned with information from the respectivecorresponding Storage Allocation and Tracking block 2814/2824. Streamingengine 125 does not explicitly manage μTLB 2812/2822. The system memorymanagement unit (MMU) invalidates μTLBs as necessary during contextswitches.

Storage Allocation and Tracking 2814/2824 manages the internal storageof the stream, discovering data reuse and tracking the lifetime of eachpiece of data. The block accepts two virtual addresses per cycle andbinds those addresses to slots in the internal storage. The data storeis organized as an array of slots. The streaming engine maintainsfollowing metadata to track the contents and lifetime of the data ineach slot: 49-bit virtual address associated with the slot, valid bitindicating valid address, ready bit indicating data has arrived for theaddress, active bit indicating if there are any references outstandingto this data, and a last reference value indicating the most recentreference to this slot in the reference queue. The storage allocationand tracking are further described herein.

Respective reference queue 2815/2825 stores the sequence of referencesgenerated by the respective corresponding address generator 2811/2821.The reference sequence enables the data formatting network to presentdata to processing unit core 110 in the correct order. Each entry inrespective reference queue 2815/2825 contains the information necessaryto read data out of the data store and align the data for processingunit core 110. Respective reference queue 2815/2825 maintains theinformation listed in Table 6 in each slot.

TABLE 6 Data Slot Low Slot number for the lower half of data associatedwith aout0 Data Slot High Slot number for the upper half of dataassociated with aout1 Rotation Number of bytes to rotate data to alignnext element with lane 0 Length Number of valid bytes in this reference

Storage allocation and tracking 2814/2824 inserts references inreference queue 2815/2825 as address generator 2811/2821 generates newaddresses. Storage allocation and tracking 2814/2824 removes referencesfrom reference queue 2815/2825 when the data becomes available and thereis room in the stream head registers. As storage allocation and tracking2814/2824 removes slot references from reference queue 2815/2825 andformats data, the references are checked for the last reference to thecorresponding slots. Storage allocation and tracking 2814/2824 comparesreference queue 2815/2825 removal pointer against the recorded lastreference of the slot. If the pointer and the recorded last referencematch, then storage allocation and tracking 2814/2824 marks the slotinactive once the data is no longer needed.

Streaming engine 125 has respective data storage 2816/2826 for aselected number of elements. Deep buffering allows the streaming engineto fetch far ahead in the stream, hiding memory system latency. Eachdata storage 2816/2826 accommodates two simultaneous read operations andtwo simultaneous write operations per cycle and each is thereforereferred to a two-read, two-write (2 r 2 w) data storage. In otherexamples, the amount of buffering can be different. In the currentexample, streaming engine 125 dedicates 32 slots to each stream witheach slot tagged by a virtual address. Each slot holds 64 bytes of datain eight banks of eight bytes.

Data storage 2816/2826 and the respective storage allocation/trackinglogic 2814/2824 and reference queues 2815/2825 implement the data FIFO1902 discussed with reference to FIG. 19.

Respective butterfly network 2817/2827 includes a seven-stage butterflynetwork. Butterfly network 2817/2827 receives 128 bytes of input andgenerates 64 bytes of output. The first stage of the butterfly isactually a half-stage that collects bytes from both slots that match anon-aligned fetch and merges the collected bytes into a single, rotated64-byte array. The remaining six stages form a standard butterflynetwork. Respective butterfly network 2817/2827 performs the followingoperations: rotates the next element down to byte lane 0; promotes datatypes by a power of two, if requested; swaps real and imaginarycomponents of complex numbers, if requested; and converts big endian tolittle endian if processing unit core 110 is presently in big endianmode. The user specifies element size, type promotion, andreal/imaginary swap as part of the parameters of the stream.

Streaming engine 125 attempts to fetch and format data ahead ofprocessing unit core 110's demand in order to maintain full throughput.Respective stream head registers 2818/2828 provide a small amount ofbuffering so that the process remains fully pipelined. Respective streamhead registers 2818/2828 are not directly architecturally visible. Eachstream also has a respective stream valid register 2819/2829. Validregisters 2819/2829 indicate which elements in the corresponding streamhead registers 2818/2828 are valid.

The two streams 2810/2820 share a pair of independent L2 interfaces2830: L2 Interface A (IFA) 2833 and L2 Interface B (IFB) 2834. Each L2interface provides 512 bits/cycle throughput direct to the L2 controller130 (FIG. 1) via respective buses 147/149 for an aggregate bandwidth of1024 bits/cycle. The L2 interfaces use the credit-based multicore busarchitecture (MBA) protocol. The MBA protocol is described in moredetail in U.S. Pat. No. 9,904,645, “Multicore Bus Architecture withNon-Blocking High Performance Transaction Credit System,” which isincorporated by reference herein. The L2 controller assigns a pool ofcommand credits to each interface. The pool has sufficient credits sothat each interface can send sufficient requests to achieve fullread-return bandwidth when reading L2 RAM, L2 cache and multicore sharedmemory controller (MSMC) memory, as described in more detail herein.

To maximize performance, in this example both streams can use both L2interfaces, allowing a single stream to send a peak command rate of tworequests per cycle. Each interface prefers one stream over the other,but this preference changes dynamically from request to request. IFA2833 and IFB 2834 prefer opposite streams, when IFA 2833 prefers Stream0, IFB 2834 prefers Stream 1 and vice versa.

Respective arbiter 2831/2832 ahead of each respective interface2833/2834 applies the following basic protocol on every cycle havingcredits available. Arbiter 2831/2832 checks if the preferred stream hasa command ready to send. If so, arbiter 2831/2832 chooses that command.Arbiter 2831/2832 next checks if an alternate stream has at least tworequests ready to send, or one command and no credits. If so, arbiter2831/2832 pulls a command from the alternate stream. If either interfaceissues a command, the notion of preferred and alternate streams swap forthe next request. Using this algorithm, the two interfaces dispatchrequests as quickly as possible while retaining fairness between the twostreams. The first rule ensures that each stream can send a request onevery cycle that has available credits. The second rule provides amechanism for one stream to borrow the interface of the other when thesecond interface is idle. The third rule spreads the bandwidth demandfor each stream across both interfaces, ensuring neither interfacebecomes a bottleneck.

Respective coarse grain rotator 2835/2836 enables streaming engine 125to support a transposed matrix addressing mode. In this mode, streamingengine 125 interchanges the two innermost dimensions of themultidimensional loop to access an array column-wise rather thanrow-wise. Respective rotators 2835/2836 are not architecturally visible.

FIG. 29 illustrates an example stream template register 2900. The streamdefinition template provides the full structure of a stream thatcontains data. The iteration counts and dimensions provide most of thestructure, while the various flags provide the rest of the details. Inthis example, a single stream template 2900 is defined for alldata-containing streams. All stream types supported by the streamingengine are covered by the template 2900. The streaming engine supports asix-level loop nest for addressing elements within the stream. Most ofthe fields in the stream template 2900 map directly to the parameters inthat algorithm. The numbers above the fields are bit numbers within a256-bit vector. Table 7 shows the stream field definitions of a streamtemplate.

TABLE 7 FIG. 29 Field Reference Size Name Number Description Bits ICNT02901 Iteration count for loop 0 32 ICNT1 2902 Iteration count for loop 132 ICNT2 2903 Iteration count for loop 2 32 ICNT3 2904 Iteration countfor loop 3 32 ICNT4 2905 Iteration count for loop 4 32 ICNT5 2906Iteration count for loop 5 32 DIM1 2911 Signed dimension for loop 1 32DIM2 2912 Signed dimension for loop 2 32 DIM3 2913 Signed dimension forloop 3 32 DIM4 2914 Signed dimension for loop 4 32 DIM5 2915 Signeddimension for loop 5 32 FLAGS 2921 Stream modifier flags 64

Loop 0 is the innermost loop and loop 5 is the outermost loop. In thecurrent example, DIM0 is equal to ELEM_BYTES defining physicallycontiguous data. Thus, the stream template register 2900 does not defineDIM0. Streaming engine 125 interprets iteration counts as unsignedintegers and dimensions as unscaled signed integers. An iteration countof zero at any level (ICNT0, ICNT1, ICNT2, ICNT3, ICNT4 or ICNT5)indicates an empty stream. Each iteration count must be at least one todefine a valid stream. The template above specifies the type ofelements, length and dimensions of the stream. The stream instructionsseparately specify a start address, e.g., by specification of a scalarregister in scalar register file 211 which stores the start address.Thus, a program can open multiple streams using the same template butdifferent registers storing the start address.

FIG. 30 illustrates an example of sub-field definitions of the flagsfield 2911 shown in FIG. 29. As shown in FIG. 30, the flags field 2911is 6 bytes or 48 bits. FIG. 30 shows bit numbers of the fields. Table 8shows the definition of these fields.

TABLE 8 FIG. 30 Reference Size Field Name Number Description Bits ELTYPE3001 Type of data element 4 TRANSPOSE 3002 Two-dimensional transposemode 3 PROMOTE 3003 Promotion mode 3 VECLEN 3004 Stream vector length 3ELDUP 3005 Element duplication 3 GRDUP 3006 Group duplication 1 DECIM3007 Element decimation 2 THROTTLE 3008 Fetch ahead throttle mode 2DIMFMT 3009 Stream dimensions format 3 DIR 3010 Stream direction 1 0forward direction 1 reverse direction CBK0 3011 First circular blocksize number 4 CBK1 3012 Second circular block size number 4 AM0 3013Addressing mode for loop 0 2 AM1 3014 Addressing mode for loop 1 2 AM23015 Addressing mode for loop 2 2 AM3 3016 Addressing mode for loop 3 2AM4 3017 Addressing mode for loop 4 2 AM5 3018 Addressing mode for loop5 2

The Element Type (ELTYPE) field 3001 defines the data type of theelements in the stream. The coding of the four bits of the ELTYPE field3001 is defined as shown in Table 9.

TABLE 9 Sub-element Size Total Element Size ELTYPE Real/Complex BitsBits 0000 real 8 8 0001 real 16 16 0010 real 32 32 0011 real 64 64 0100reserved 0101 reserved 0110 reserved 0111 reserved 1000 complex 8 16 noswap 1001 complex 16 32 no swap 1010 complex 32 64 no swap 1011 complex64 128 no swap 1100 complex 8 16 swapped 1101 complex 16 32 swapped 1110complex 32 64 swapped 1111 complex 64 128 swapped

Real/Complex Type determines whether the streaming engine treats eachelement as a real number or two parts (real/imaginary ormagnitude/angle) of a complex number and also specifies whether to swapthe two parts of complex numbers. Complex types have a total elementsize twice the sub-element size. Otherwise, the sub-element size equalsthe total element size.

Sub-Element Size determines the type for purposes of type promotion andvector lane width. For example, 16-bit sub-elements get promoted to32-bit sub-elements or 64-bit sub-elements when a stream requests typepromotion. The vector lane width matters when processing unit core 110(FIG. 1) operates in big endian mode, as the core 110 lays out vectorsin little endian order.

Total Element Size specifies the minimal granularity of the stream whichdetermines the number of bytes the stream fetches for each iteration ofthe innermost loop. Streams read whole elements, either in increasing ordecreasing order. Therefore, the innermost dimension of a stream spansICNT0×total-element-size bytes.

The TRANSPOSE field 3002 determines whether the streaming engineaccesses the stream in a transposed order. The transposed orderexchanges the inner two addressing levels. The TRANSPOSE field 3002 alsoindicated the granularity for transposing the stream. The coding of thethree bits of the TRANSPOSE field 3002 is defined as shown in Table 10for normal 2D operations.

TABLE 10 Transpose Meaning 000 Transpose disabled 001 Transpose on 8-bitboundaries 010 Transpose on 16-bit boundaries 011 Transpose on 32-bitboundaries 100 Transpose on 64-bit boundaries 101 Transpose on 128-bitboundaries 110 Transpose on 256-bit boundaries 111 Reserved

Streaming engine 125 can transpose data elements at a differentgranularity than the element size thus allowing programs to fetchmultiple columns of elements from each row. The transpose granularitycannot be smaller than the element size. The TRANSPOSE field 3002interacts with the DIMFMT field 3009 in a manner further describedbelow.

The PROMOTE field 3003 controls whether the streaming engine promotessub-elements in the stream and the type of promotion. When enabled,streaming engine 125 promotes types by powers-of-2 sizes. The coding ofthe three bits of the PROMOTE field 3003 is defined as shown in Table11.

TABLE 11 Promotion Promotion Resulting Sub-element Size PROMOTE FactorType  8-bit 16-bit 32-bit 64-bit 000 1x N/A  8-bit 16-bit 32-bit 64-bit001 2x zero extend 16-bit 32-bit 64-bit Invalid 010 4x zero extend32-bit 64-bit Invalid Invalid 011 8x zero extend 64-bit Invalid InvalidInvalid 100 reserved 101 2x sign extend 16-bit 32-bit 64-bit Invalid 1104x sign extend 32-bit 64-bit Invalid Invalid 111 8x sign extend 64-bitInvalid Invalid Invalid

When PROMOTE is 000, corresponding to a 1× promotion, each sub-elementis unchanged and occupies a vector lane equal in width to the sizespecified by ELTYPE. When PROMOTE is 001, corresponding to a 2×promotion and zero extend, each sub-element is treated as an unsignedinteger and zero extended to a vector lane twice the width specified byELTYPE. A 2× promotion is invalid for an initial sub-element size of 64bits. When PROMOTE is 010, corresponding to a 4× promotion and zeroextend, each sub-element is treated as an unsigned integer and zeroextended to a vector lane four times the width specified by ELTYPE. A 4×promotion is invalid for an initial sub-element size of 32 or 64 bits.When PROMOTE is 011, corresponding to an 8× promotion and zero extend,each sub-element is treated as an unsigned integer and zero extended toa vector lane eight times the width specified by ELTYPE. An 8× promotionis invalid for an initial sub-element size of 16, 32 or 64 bits. WhenPROMOTE is 101, corresponding to a 2× promotion and sign extend, eachsub-element is treated as a signed integer and sign extended to a vectorlane twice the width specified by ELTYPE. A 2× promotion is invalid foran initial sub-element size of 64 bits. When PROMOTE is 110,corresponding to a 4× promotion and sign extend, each sub-element istreated as a signed integer and sign extended to a vector lane fourtimes the width specified by ELTYPE. A 4× promotion is invalid for aninitial sub-element size of 32 or 64 bits. When PROMOTE is 111,corresponding to an 8× promotion and zero extend, each sub-element istreated as a signed integer and sign extended to a vector lane eighttimes the width specified by ELTYPE. An 8× promotion is invalid for aninitial sub-element size of 16, 32 or 64 bits.

The VECLEN field 3004 defines the stream vector length for the stream inbytes. Streaming engine 125 breaks the stream into groups of elementsthat are VECLEN bytes long. The coding of the three bits of the VECLENfield 3004 is defined as shown in Table 12.

TABLE 12 VECLEN Stream Vector Length 000 1 byte 001 2 bytes 010 4 bytes011 8 bytes 100 16 bytes 101 32 bytes 110 64 bytes 111 Reserved

VECLEN cannot be less than the product of the element size in bytes andthe duplication factor. As shown in Table 11, the maximum VECLEN of 64bytes equals the preferred vector size of vector data path side B 116.When VECLEN is shorter than the native vector width of processing unitcore 110, streaming engine 125 pads the extra lanes in the vectorprovided to processing unit core 110. The GRDUP field 3006 determinesthe type of padding. The VECLEN field 3004 interacts with ELDUP field3005 and GRDUP field 3006 in a manner detailed below.

The ELDUP field 3005 specifies the number of times to duplicate eachelement. The element size multiplied with the element duplication amountcannot exceed the 64 bytes. The coding of the three bits of the ELDUPfield 3005 is defined as shown in Table 13.

TABLE 13 ELDUP Duplication Factor 000 No Duplication 001  2 times 010  4times 011  8 times 100 16 times 101 32 times 110 64 times 111 Reserved

The ELDUP field 3005 interacts with VECLEN field 3004 and GRDUP field3006 in a manner detailed below. The nature of the relationship betweenthe permitted element size, the element duplication factor, and thedestination vector length requires that a duplicated element thatoverflows the first destination register fills an integer number ofdestination registers upon completion of duplication. The data of theadditional destination registers eventually supplies the respectivestream head register 2818/2828. Upon completion of duplication of afirst data element, the next data element is rotated down to the leastsignificant bits of source register 3100 discarding the first dataelement. The process then repeats for the new data element.

The GRDUP bit 3006 determines whether group duplication is enabled. IfGRDUP bit 3006 is 0, then group duplication is disabled. If the GRDUPbit 3006 is 1, then group duplication is enabled. When enabled by GRDUPbit 3006, streaming engine 125 duplicates a group of elements to fillthe vector width. VECLEN field 3004 defines the length of the group toreplicate. When VECLEN field 3004 is less than the vector length ofprocessing unit core 110 and GRDUP bit 3006 enables group duplication,streaming engine 125 fills the extra lanes (see FIGS. 21 and 22) withadditional copies of the stream vector. Because stream vector length andvector length of processing unit core 110 are integral powers of two,group duplication produces an integral number of duplicate copies. NoteGRDUP and VECLEN do not specify the number of duplications. The numberof duplications performed is based upon the ratio of VECLEN to thenative vector length, which is 64 bytes/512 bits in this example.

The GRDUP field 3006 specifies how stream engine 125 pads stream vectorsfor bits following the VECLEN length to the vector length of processingunit core 110. When GRDUP bit 3006 is 0, streaming engine 125 fills theextra lanes with zeros and marks the extra vector lanes invalid. WhenGRDUP bit 3006 is 1, streaming engine 125 fills extra lanes with copiesof the group of elements in each stream vector. Setting GRDUP bit 3006to 1 has no effect when VECLEN is set to the native vector width ofprocessing unit core 110. VECLEN must be at least as large as theproduct of ELEM_BYTES and the element duplication factor ELDUP. That is,an element or the duplication factor number of elements cannot beseparated using VECLEN.

Group duplication operates to the destination vector size. Groupduplication does not change the data supplied when the product of theelement size ELEM_BYTES and element duplication factor ELDUP equals orexceeds the destination vector width. Under such conditions, the statesof the GRDUP bit 3006 and the VECLEN field 3004 have no effect on thesupplied data.

The set of examples below illustrate the interaction between VECLEN andGRDUP. Each of the following examples show how the streaming engine mapsa stream onto vectors across different stream vector lengths and thevector size of vector data path side B 116. The stream of this exampleincludes twenty-nine elements (E0 to E28) of 64 bits/8 bytes. The streamcan be a linear stream of twenty-nine elements or an inner loop of 29elements. The tables illustrate eight byte lanes such as shown in FIG.21. Each illustrated vector is stored in the respective stream headregister 2818/2828 in turn.

Table 14 illustrates how the example stream maps onto bits within the64-byte processor vectors when VECLEN is 64 bytes.

TABLE 14 Processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 E7 E6 E5 E4 E3 E2 E1 E0 2 E15 E14 E13 E12 E11 E10 E9 E8 3E23 E22 E21 E20 E19 E18 E17 E16 4 0 0 0 E28 E27 E26 E25 E24

As shown in Table 14, the stream extends over four vectors. Aspreviously described, the lanes within vector 4 that extend beyond thestream are zero filled. When VECLEN has a size equal to the nativevector length, the value of GRDUP does not matter as no duplication cantake place with such a VECLEN.

Table 15 shows the same parameters as shown in Table 20, except withVECLEN of 32 bytes. Group duplicate is disabled (GRDUP=0).

TABLE 15 Processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 0 0 0 0 E3 E2 E1 E0 2 0 0 0 0 E7 E6 E5 E4 3 0 0 0 0 E11 E10E9 E8 4 0 0 0 0 E15 E14 E13 E12 5 0 0 0 0 E19 E18 E17 E16 6 0 0 0 0 E23E22 E21 E20 7 0 0 0 0 E27 E26 E25 E24 8 0 0 0 0 0 0 0 E28

The twenty-nine elements of the stream are distributed over lanes 0 to 3in eight vectors. Extra lanes 4 to 7 in vectors 1-7 are zero filled. Invector 8, lane 1 has a stream element (E28) and the other lanes are zerofilled.

Table 16 shows the same parameters as shown in Table 22, except withVECLEN of sixteen bytes. Group duplicate is disabled (GRDUP=0).

TABLE 16 Processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 0 0 0 0 0 0 E1 E0 2 0 0 0 0 0 0 E3 E2 3 0 0 0 0 0 0 E5 E4 40 0 0 0 0 0 E7 E6 5 0 0 0 0 0 0 E9 E8 6 0 0 0 0 0 0 E11 E10 7 0 0 0 0 00 E13 E12 8 0 0 0 0 0 0 E15 E14 9 0 0 0 0 0 0 E17 E16 10 0 0 0 0 0 0 E19E18 11 0 0 0 0 0 0 E21 E20 12 0 0 0 0 0 0 E23 E22 13 0 0 0 0 0 0 E25 E2414 0 0 0 0 0 0 E27 E26 15 0 0 0 0 0 0 0 E28

The twenty-nine elements of the stream are distributed over lane 0 andlane 1 in fifteen vectors. Extra lanes 2 to 7 in vectors 1-14 are zerofilled. In vector 15, lane 1 has a stream element (E28) and the otherlanes are zero filled.

Table 17 shows the same parameters as shown in Table 14, except withVECLEN of eight bytes. Group duplicate is disabled (GRDUP=0).

TABLE 17 Processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 0 0 0 0 0 0 0 E0 2 0 0 0 0 0 0 0 E1 3 0 0 0 0 0 0 0 E2 4 0 00 0 0 0 0 E3 5 0 0 0 0 0 0 0 E4 6 0 0 0 0 0 0 0 E5 7 0 0 0 0 0 0 0 E6 80 0 0 0 0 0 0 E7 9 0 0 0 0 0 0 0 E8 10 0 0 0 0 0 0 0 E9 11 0 0 0 0 0 0 0E10 12 0 0 0 0 0 0 0 E11 13 0 0 0 0 0 0 0 E12 14 0 0 0 0 0 0 0 E13 15 00 0 0 0 0 0 E14 16 0 0 0 0 0 0 0 E15 17 0 0 0 0 0 0 0 E16 18 0 0 0 0 0 00 E17 19 0 0 0 0 0 0 0 E18 20 0 0 0 0 0 0 0 E19 21 0 0 0 0 0 0 0 E20 220 0 0 0 0 0 0 E21 23 0 0 0 0 0 0 0 E22 24 0 0 0 0 0 0 0 E23 25 0 0 0 0 00 0 E24 26 0 0 0 0 0 0 0 E25 27 0 0 0 0 0 0 0 E26 28 0 0 0 0 0 0 0 E2729 0 0 0 0 0 0 0 E28

The twenty-nine elements of the stream appear in lane 0 in twenty-ninevectors. Extra lanes 1-7 in vectors 1-29 are zero filled.

Table 18 shows the same parameters as shown in Table 15, except withVECLEN of thirty-two bytes and group duplicate is enabled (GRDUP=1).

TABLE 18 Processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 E3 E2 E1 E0 E3 E2 E1 E0 2 E7 E6 E5 E4 E7 E6 E5 E4 3 E11 E10E9 E8 E11 E10 E9 E8 4 E15 E14 E13 E12 E15 E14 E13 E12 5 E19 E18 E17 E16E19 E18 E17 E16 6 E23 E22 E21 E20 E23 E22 E21 E20 7 E27 E26 E25 E24 E27E26 E25 E24 8 0 0 0 E28 0 0 0 E28

The twenty-nine elements of the stream are distributed over lanes 0-7 ineight vectors. Each vector 1-7 includes four elements duplicated. Theduplication factor (2) results because VECLEN (32 bytes) is half thenative vector length of 64 bytes. In vector 8, lane 0 has a streamelement (E28) and lanes 1-3 are zero filled. Lanes 4-7 of vector 9duplicate this pattern.

Table 19 shows the same parameters as shown in Table 16, except withVECLEN of sixteen bytes. Group duplicate is enabled (GRDUP=1).

TABLE 19 processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 E1 E0 E1 E0 E1 E0 E1 E0 2 E3 E2 E3 E2 E3 E2 E3 E2 3 E5 E4 E5E4 E5 E4 E5 E4 4 E7 E6 E7 E6 E7 E6 E7 E6 5 E9 E8 E9 E8 E9 E8 E9 E8 6 E11E10 E11 E10 E11 E10 E11 E10 7 E13 E12 E13 E12 E13 E12 E13 E12 8 E15 E14E15 E14 E15 E14 E15 E14 9 E17 E16 E17 E16 E17 E16 E17 E16 10 E19 E18 E19E18 E19 E18 E19 E18 11 E21 E20 E21 E20 E21 E20 E21 E20 12 E23 E22 E23E22 E23 E22 E23 E22 13 E25 E24 E25 E24 E25 E24 E25 E24 14 E27 E26 E27E26 E27 E26 E27 E26 15 0 E28 0 E28 0 E28 0 E28

The twenty-nine elements of the stream are distributed over lanes 0-7 infifteen vectors. Each vector 1-7 includes two elements duplicated fourtimes. The duplication factor (4) results because VECLEN (16 bytes) isone quarter the native vector length of 64 bytes. In vector 15, lane 0has a stream element (E28) and lane 1 is zero filled. This pattern isduplicated in lanes 2 and 3, lanes 4 and 5, and lanes 6 and 7 of vector15.

Table 20 shows the same parameters as shown in Table 17, except withVECLEN of eight bytes. Group duplicate is enabled (GRDUP=1).

TABLE 20 Processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 E0 E0 E0 E0 E0 E0 E0 E0 2 E1 E1 E1 E1 E1 E1 E1 E1 3 E2 E2 E2E2 E2 E2 E2 E2 4 E3 E3 E3 E3 E3 E3 E3 E3 5 E4 E4 E4 E4 E4 E4 E4 E4 6 E5E5 E5 E5 E5 E5 E5 E5 7 E6 E6 E6 E6 E6 E6 E6 E6 8 E7 E7 E7 E7 E7 E7 E7 E79 E8 E8 E8 E8 E8 E8 E8 E8 10 E9 E9 E9 E9 E9 E9 E9 E9 11 E10 E10 E10 E10E10 E10 E10 E10 12 E11 E11 E11 E11 E11 E11 E11 E11 13 E12 E12 E12 E12E12 E12 E12 E12 14 E13 E13 E13 E13 E13 E13 E13 E13 15 E14 E14 E14 E14E14 E14 E14 E14 16 E15 E15 E15 E15 E15 E15 E15 E15 17 E16 E16 E16 E16E16 E16 E16 E16 18 E17 E17 E17 E17 E17 E17 E17 E17 19 E18 E18 E18 E18E18 E18 E18 E18 20 E19 E19 E19 E19 E19 E19 E19 E19 21 E20 E20 E20 E20E20 E20 E20 E20 22 E21 E21 E21 E21 E21 E21 E21 E21 23 E22 E22 E22 E22E22 E22 E22 E22 24 E23 E23 E23 E23 E23 E23 E23 E23 25 E24 E24 E24 E24E24 E24 E24 E24 26 E25 E25 E25 E25 E25 E25 E25 E25 27 E26 E26 E26 E26E26 E26 E26 E26 28 E27 E27 E27 E27 E27 E27 E27 E27 29 E28 E28 E28 E28E28 E28 E28 E28

The twenty-nine elements of the stream all appear on lanes 0 to 7 intwenty-nine vectors. Each vector includes one element duplicated eighttimes. The duplication factor (8) results because VECLEN (8 bytes) isone eighth the native vector length of 64 bytes. Thus, each lane is thesame in vectors 1-29.

FIG. 31 illustrates an example of vector length masking/groupduplication block 2025 (see FIG. 20) that is included within formatterblock 1903 of FIG. 19. Input register 3100 receives a vector input fromelement duplication block 2024 shown in FIG. 20. Input register 3100includes 64 bytes arranged in 64 1-byte blocks byte0 to byte63. Notethat bytes byte0 to byte63 are each equal in length to the minimum ofELEM_BYTES. A set of multiplexers 3101 to 3163 couple input bytes fromsource register 3100 to output register 3170. Each respectivemultiplexer 3101 to 3163 supplies an input to a respective byte1 tobyte63 of output register 3170. Not all input bytes byte0 to byte63 ofinput register 3100 are coupled to every multiplexer 3101 to 3163. Notethere is no multiplexer supplying byte0 of output register 3170. In thisexample, byte0 of output register 3170 is supplied by byte0 of inputregister 3100.

Multiplexers 3101 to 3163 are controlled by multiplexer control encoder3180. Multiplexer control encoder 3180 receives ELEM_BYTES, VECLEN andGRDUP input signals and generates respective control signals formultiplexers 3101 to 3163. ELEM_BYTES and ELDUP are supplied tomultiplexer control encoder 3180 to check to see that VECLEN is at leastas great as the product of ELEM_BYTES and ELDUP. In operation,multiplexer control encoder 3180 controls multiplexers 3101 to 3163 totransfer least significant bits equal in number to VECLEN from inputregister 3100 to output register 3170. If GRDUP=0 indicating groupduplication disabled, then multiplexer control encoder 3180 controls theremaining multiplexers 3101 to 3163 to transfer zeros to all bits in theremaining most significant lanes of output register 3170. If GRDUP=1indicating group duplication enabled, then multiplexer control encoder3180 controls the remaining multiplexers 3101 to 3163 to duplicate theVECLEN number of least significant bits of input register 3100 into themost significant lanes of output register 3170. This control is similarto the element duplication control described above and fills the outputregister 3170 with the first vector. For the next vector, data withininput register 3100 is rotated down by VECLEN, discarding the previousVECLEN least significant bits. The rate of data movement in formatter1903 (FIG. 19) is set by the rate of consumption of data by processingunit core 110 (FIG. 1) via stream read and advance instructionsdescribed below. The group duplication formatting repeats as long as thestream includes additional data elements.

Element duplication (ELDUP) and group duplication (GRUDP) areindependent. Note these features include independent specification andparameter setting. Thus, element duplication and group duplication canbe used together or separately. Because of how these are specified,element duplication permits overflow to the next vector while groupduplication does not.

Referring again to FIG. 30, the DECIM field 3007 controls data elementdecimation of the corresponding stream. Streaming engine 125 deletesdata elements from the stream upon storage in respective stream headregisters 2818/2828 for presentation to the requesting functional unit.Decimation removes whole data elements, not sub-elements. The DECIMfield 3007 is defined as listed in Table 21.

TABLE 21 DECIM Decimation Factor 00 No Decimation 01 2 times 10 4 times11 Reserved

If DECIM field 3007 equals 00, then no decimation occurs. The dataelements are passed to the corresponding stream head registers 2818/2828without change. If DECIM field 3007 equals 01, then 2:1 decimationoccurs. Streaming engine 125 removes odd number elements from the datastream upon storage in the stream head registers 2818/2828. Limitationsin the formatting network require 2:1 decimation to be employed withdata promotion by at least 2× (PROMOTE cannot be 000), ICNT0 must bemultiple of 2, and the total vector length (VECLEN) must be large enoughto hold a single promoted, duplicated element. For transposed streams(TRANSPOSE≠0), the transpose granule must be at least twice the elementsize in bytes before promotion. If DECIM field 3007 equals 10, then 4:1decimation occurs. Streaming engine 125 retains every fourth dataelement removing three elements from the data stream upon storage in thestream head registers 2818/2828. Limitations in the formatting networkrequire 4:1 decimation to be employed with data promotion by at least 4×(PROMOTE cannot be 000, 001 or 101), ICNT0 must be a multiple of 4 andthe total vector length (VECLEN) must be large enough to hold a singlepromoted, duplicated element. For transposed streams (TRANSPOSE≠0), inone example, decimation removes columns, and does not remove rows. Thus,in such cases, the transpose granule must be at least twice the elementsize in bytes before promotion for 2:1 decimation (GRANULE≥2×ELEM_BYTES)and at least four times the element size in bytes before promotion for4:1 decimation (GRANULE≥4×ELEM_BYTES).

The THROTTLE field 3008 controls how aggressively the streaming enginefetches ahead of processing unit core 110. The coding of the two bits ofthis field is defined as shown in Table 22.

TABLE 22 THROTTLE Description 00 Minimum throttling, maximum fetch ahead01 Less throttling, more fetch ahead 10 More throttling, less fetchahead 11 Maximum throttling, minimum fetch ahead

THROTTLE does not change the meaning of the stream and serves only as ahint. The streaming engine can ignore this field. Programs should notrely on the specific throttle behavior for program correctness, becausethe architecture does not specify the precise throttle behavior.THROTTLE allows programmers to provide hints to the hardware about theprogram behavior. By default, the streaming engine attempts to get asfar ahead of processing unit core 110 as possible to hide as muchlatency as possible (equivalent to THROTTLE=11), while providing fullstream throughput to processing unit core 110. While some applicationsneed this level of throughput, such throughput can cause bad systemlevel behavior for others. For example, the streaming engine discardsall fetched data across context switches. Therefore, aggressivefetch-ahead can lead to wasted bandwidth in a system with large numbersof context switches.

The DIMFMT field 3009 defines which of the loop count fields ICNT0 2901,ICNT1 2902, ICNT2 2903, ICNT3 2804, ICNT4 2905 and ICNT5 2906, of theloop dimension fields DIM1 2911, DIM2 2912, DIM3 2913, DIM4 2914 andDIM5 2915 and of the addressing mode fields AM0 3013, AM1 3014, AM23015, AM3 3016, AM4 3017 and AM5 3018 (part of FLAGS field 2921) of thestream template register 2900 are active for the particular stream.Table 23 lists the active loops for various values of the DIMFMT field3009. Each active loop count must be at least 1 and the outer activeloop count must be greater than 1.

TABLE 23 DIMFMT Loop5 Loop4 Loop3 Loop2 Loop1 Loop0 000 InactiveInactive Inactive Inactive Inactive Active 001 Inactive InactiveInactive Inactive Active Active 010 Inactive Inactive Inactive ActiveActive Active 011 Inactive Inactive Active Active Active Active 100Inactive Active Active Active Active Active 101 Active Active ActiveActive Active Active 110-111 Reserved

The DIR bit 3010 determines the direction of fetch of the inner loop(Loop0). If the DIR bit 3010 is 0, Loop0 fetches are in the forwarddirection toward increasing addresses. If the DIR bit 3010 is 1, Loop0fetches are in the backward direction toward decreasing addresses. Thefetch direction of other loops is determined by the sign of thecorresponding loop dimension DIM1, DIM2, DIM3, DIM4 and DIM5.

The CBK0 field 3011 and the CBK1 field 3012 control the circular blocksize upon selection of circular addressing. The manner of determiningthe circular block size is described herein.

The AM0 field 3013, AM1 field 3014, AM2 field 3015, AM3 field 3016, AM4field 3017 and AM5 field 3018 control the addressing mode of acorresponding loop, thus permitting the addressing mode to beindependently specified for each loop. Each of AM0 field 3013, AM1 field3014, AM2 field 3015, AM3 field 3016, AM4 field 3017 and AM5 field 3018are three bits and are decoded as listed in Table 24.

TABLE 24 AMx field Meaning 00 Linear addressing 01 Circular addressingblock size set by CBK0 10 Circular addressing block size set by CBK0 +CBK1 + 1 11 reservedIn linear addressing, the address advances according to the addressarithmetic whether forward or reverse. In circular addressing, theaddress remains within a defined address block. Upon reaching the end ofthe circular address block the address wraps around to the beginninglimit of the block. Circular addressing blocks are limited to 2Naddresses where N is an integer. Circular address arithmetic can operateby cutting the carry chain between bits and not allowing a selectednumber of most significant bits to change. Thus, arithmetic beyond theend of the circular block changes only the least significant bits. Theblock size is set as listed in Table 25.

TABLE 25 Encoded Block Size CBK0 or CBK0 + CBK1 + 1 Block Size (bytes) 0512 1  1K 2  2K 3  4K 4  8K 5  16K 6  32K 7  64K 8 128K 9 256K 10 512K11  1M 12  2M 13  4M 14  8M 15  16M 16  32M 17  64M 18 128M 19 256M 20512M 21  1 G 22  2 G 23  4 G 24  8 G 25  16 G 26  32 G 27  64 G 28Reserved 29 Reserved 30 Reserved 31 Reserved

In this example, the circular block size is set by the number encoded byCBK0 (first circular address mode 01) or the number encoded byCBK0+CBK1+1 (second circular address mode 10). For example, in the firstcircular address mode, the circular address block size can range from512 bytes to 16 M bytes. For the second circular address mode, thecircular address block size can range from 1 K bytes to 64 G bytes.Thus, the encoded block size is 2^((B+9)) bytes, where B is the encodedblock number which is CBK0 for the first block size (AMx of 01) andCBK0+CBK1+1 for the second block size (AMx of 10).

The processing unit 110 (FIG. 1) exposes the streaming engine 125 (FIG.28) to programs through a small number of instructions and specializedregisters. Programs start and end streams with SEOPEN and SECLOSE.SEOPEN opens a new stream and the stream remains open until terminatedexplicitly by SECLOSE or replaced by a new stream with SEOPEN. TheSEOPEN instruction specifies a stream number indicating opening stream 0or stream 1. The SEOPEN instruction specifies a data register storingthe start address of the stream. The SEOPEN instruction also specifies astream template register that stores the stream template as describedabove. The arguments of the SEOPEN instruction are listed in Table 26.

TABLE 26 Argument Description Stream Start Address Scalar registerstoring stream start address Register Stream Number Stream 0 or Stream 1Stream Template Register Vector register storing stream template data

The stream start address register is a register in general scalarregister file 211 (FIG. 2) in this example. The SEOPEN instruction canspecify the stream start address register via scr1 field 1305 (FIG. 13)of example instruction coding 1300 (FIG. 13). The SEOPEN instructionspecifies stream 0 or stream 1 in the opcode. The stream templateregister is a vector register in general vector register file 221 inthis example. The SEOPEN instruction can specify the stream templateregister via scr2/cst field 1304 (FIG. 13). If the specified stream isactive, the SEOPEN instruction closes the prior stream and replaces thestream with the specified stream.

SECLOSE explicitly marks a stream inactive, flushing any outstandingactivity. Any further references to the stream trigger exceptions.SECLOSE also allows a program to prematurely terminate one or bothstreams.

An SESAVE instruction saves the state of a stream by capturingsufficient state information of a specified stream to restart thatstream in the future. An SERSTR instruction restores a previously savedstream. An SESAVE instruction saves the stream metadata and does notsave any of the stream data. The stream re-fetches stream data inresponse to an SERSTR instruction.

Each stream can be in one of three states: inactive, active, or frozenafter reset. Both streams begin in the inactive state. Opening a streammoves the stream to the active state. Closing the stream returns thestream to the inactive state. In the absence of interrupts andexceptions, streams ordinarily do not make other state transitions. Toaccount for interrupts, the streaming engine adds a third state: frozen.The frozen state represents an interrupted active stream.

In this example, four bits, two bits per stream, define the state ofboth streams. One bit per stream resides within the streaming engine,and the other bit resides within the processor core 110. The streamingengine internally tracks whether each stream holds a parameter setassociated with an active stream. This bit distinguishes an inactivestream from a not-inactive stream. The processor core 110 separatelytracks the state of each stream with a dedicated bit per stream in theTask State Register (TSR): TSR.SE0 for stream 0, and TSR.SE1 forstream 1. These bits distinguish between active and inactive streams.

Opening a stream moves the stream to the active state. Closing a streammoves the stream to the inactive state. If a program opens a new streamover a frozen stream, the new stream replaces the old stream and thestreaming engine discards the contents of the previous stream. Thestreaming engine supports opening a new stream on a currently activestream. The streaming engine discards the contents of the previousstream, flushes the pipeline, and starts fetching data for the newopened stream. Data to processor is asserted once the data has returned.If a program closes an already closed stream, nothing happens. If aprogram closes an open or frozen stream, the streaming engine discardsall state related to the stream, clears the internal stream-active bit,and clears the counter, tag and address registers. Closing a streamserves two purposes. Closing an active stream allows a program tospecifically state the stream and the resources associated with thestream are no longer needed. Closing a frozen stream also allows contextswitching code to clear the state of the frozen stream, so that othertasks do not see it.

As noted above, there are circumstances when some data within a streamholding register 2818 or 2828 is not valid. As described above, such astate can occur at the end of an inner loop when the number of streamelements is less than the respective stream holding register 2818/2828size or at the end of an inner loop when the number of stream elementsremaining is less than the lanes defined by VECLEN. For times not at theend of an inner loop, if VECLEN is less than the width of stream holdingregister 2818/2828 and GRDUP is disabled, then lanes in stream holdingregister 2818/2828 in excess of VECLEN are invalid.

Referring again to FIG. 28, in this example streaming engine 125 furtherincludes valid registers 2819 and 2829. Valid register 2819 indicatesthe valid lanes in stream head register 2818. Valid register 2829indicates the valid lanes in stream head register 2828. Respective validregisters 2819/2829 include one bit for each minimum ELEM_BYTES lanewithin the corresponding stream head register 2818/2828. In thisexample, the minimum ELEM_BYTES is 1 byte. The preferred data path widthof processor 100 and the data length of stream head registers 2818/2828is 64 bytes (512 bits). Valid registers 2819/2829 accordingly have adata width of 64 bits. Each bit in valid registers 2819/2829 indicateswhether a corresponding byte in stream head registers 2818/2828 isvalid. In this example, a 0 indicates the corresponding byte within thestream head register is invalid, and a 1 indicates the correspondingbyte is valid.

In this example, upon reading a respective one of the stream headregisters 2818/2828 and transferring of data to the requestingfunctional unit, the invalid/valid data in the respective valid register2819/2829 is automatically transferred to a data register withinpredicate register file 234 (FIG. 2) corresponding to the particularstream. In this example the valid data for stream 0 is stored inpredicate register P0 and the valid data for stream 1 is stored inpredicate register P1.

The valid data stored in the predicate register file 234 can be used ina variety of ways. The functional unit can combine the vector streamdata with another set of vectors and then store the combined data tomemory using the valid data indications as a mask, thus enabling thesame process to be used for the end of loop data as is used for caseswhere all the lanes are valid which avoids storing invalid data. Thevalid indication stored in predicate register file 234 can be used as amask or an operand in other processes. P unit 246 (FIG. 2) can have aninstruction to count the number of l's in a predicate register (BITCNT,which can be used to determine the count of valid data elements from apredicate register.

FIG. 32 illustrates example hardware 3200 to produce the valid/invalidindications stored in the valid register 2819 (FIG. 28). FIG. 32illustrates hardware for stream 0; stream 1 includes correspondinghardware. Hardware 3200 operates to generate one valid word each timedata is updated in stream head register 2818 (FIG. 28). A first inputELTYPE is supplied to decoder 3201. Decoder 3201 produces an outputTOTAL ELEMENT SIZE corresponding to the minimum data size based upon theelement size ELEM_BYTES and whether the elements are real numbers orcomplex numbers. The meanings of various codings of ELTYPE are shown inTable 9. Table 27 shows an example output of decoder 3201 in bytes forthe various ELTYPE codings. Note Table 9 lists bits and Table 27 listsbytes. As shown in Table 27, TOTAL ELEMENT SIZE is 1, 2, 4 or 8 bytes ifthe element is real and 2, 4, 8 or 16 bytes if the element is complex.

TABLE 27 Total Element Size ELTYPE Real/Complex Bytes 0000 Real 1 0001Real 2 0010 Real 4 0011 Real 8 0100 Reserved Reserved 0101 ReservedReserved 0110 Reserved Reserved 0110 Reserved Reserved 1000 Complex, NotSwapped 2 1001 Complex, Not Swapped 4 1010 Complex, Not Swapped 8 1011Complex, Not Swapped 16 1100 Complex, Swapped 2 1101 Complex, Swapped 41110 Complex, Swapped 8 1111 Complex, Swapped 16

A second input PROMOTE is supplied to decoder 3202. Decoder 3202produces an output promotion factor corresponding to the PROMOTE input.The meaning of various codings of PROMOTE are shown in Table 28, whichshows an example output of decoder 3202 in bytes for the various PROMOTEcodings. The difference in extension type (zero extension or signextension) is not relevant to decoder 3202.

TABLE 28 Promotion PROMOTE Factor 000 1 001 2 010 4 011 8 100 Reserved101 2 110 4 111 8

The outputs of decoders 3201 and 3202 are supplied to multiplier 3203.The product produced by multiplier 3203 is the lane size correspondingto the TOTAL ELEMENT SIZE and the promotion factor. Because thepromotion factor is an integral power of 2 (2^(N)), the multiplicationcan be achieved by corresponding shifting of the TOTAL ELEMENT SIZE,e.g., no shift for a promotion factor of 1, a one-bit shift for apromotion factor of 2, a two-bit shift for a promotion factor of 4, anda three-bit shift for a promotion factor of 8.

NUMBER OF LANES unit 3204 receives the vector length VECLEN and the LANESIZE and generates the NUMBER OF LANES. Table 29 shows an exampledecoding of the number of lanes for lane size in bytes and the vectorlength VECLEN.

TABLE 29 VECLEN LANE SIZE 000 001 010 011 100 101 110 1 1 2 4 8 16 32 642 — 1 2 4 8 16 32 4 — — 1 2 4 8 16 8 — — — 1 2 4 8 16 — — — — 1 2 4 32 —— — — — 1 2 64 — — — — — — 1

As previously stated, VECLEN must be greater than or equal to theproduct of the element size and the duplication factor. As shown inTable 29, VECLEN must also be greater than or equal to the product ofthe element size and the promotion factor. This means that VECLEN mustbe large enough to guarantee that an element cannot be separated fromits extension produced by type promotion block 2022 (FIG. 20). The cellsbelow the diagonal in Table 29 marked “-” indicate an unpermittedcombination of parameters.

The NUMBER OF LANES output of unit 3204 serves as one input toLANE/REMAINING ELEMENTS CONTROL WORD unit 3211. A second input comesfrom multiplexer 3212. Multiplexer 3212 receives a Loop0 input and aLoop1 input. The Loop0 input and the Loop1 input represent the number ofremaining elements in the current iteration of the corresponding loop.

FIG. 33 illustrates a partial schematic view of address generator 2811shown in FIG. 28. Address generator 2811 forms an address for fetchingthe next element in the defined stream of the corresponding streamingengine. Start address register 3301 stores a start address of the datastream. As previously described above, in this example, start addressregister 3301 is a scalar register in global scalar register file 211designated by the SEOPEN instruction that opened the correspondingstream. The start address can be copied from the specified scalarregister and stored locally at the respective address generator2811/2821 by control logic included with address generator 2811. Thefirst loop of the stream employs Loop0 count register 3311, adder 3312,multiplier 3313 and comparator 3314. Loop0 count register 3311 storesthe working copy of the iteration count of the first loop (Loop0). Foreach iteration of Loop0, adder 3312, as triggered by the Next Addresssignal, adds 1 to the loop count, which is stored back in Loop0 countregister 3311. Multiplier 3313 multiplies the current loop count and thequantity ELEM_BYTES. ELEM_BYTES is the size of each data element inloop0 in bytes. Loop0 traverses data elements physically contiguous inmemory with an iteration step size of ELEM_BYTES.

Comparator 3314 compares the count stored in Loop0 count register 3311(after incrementing by adder 3313) with the value of ICNT0 2901 (FIG.29) from the corresponding stream template register 2900 (FIG. 29). Whenthe output of adder 3312 equals the value of ICNT0 2901 of the streamtemplate register 2900, an iteration of Loop0 is complete. Comparator3314 generates an active Loop0 End signal. Loop0 count register 3311 isreset to 0 and an iteration of the next higher loop, in this case Loop1,is triggered.

Circuits for the higher loops (Loop1, Loop2, Loop3, Loop4 and Loop5) aresimilar to that illustrated in FIG. 33. Each loop includes a respectiveworking loop count register, adder, multiplier and comparator. The adderof each loop is triggered by the loop end signal of the prior loop. Thesecond input to each multiplier is the corresponding dimension DIM1,DIM2, DIM3, DIM4 and DIM5 from the corresponding stream template. Thecomparator of each loop compares the working loop register count withthe corresponding iteration value ICNT1, ICNT2, ICNT3, ICNT4 and ICNT5of the corresponding stream template register 2900. A loop end signalgenerates an iteration of the next higher loop. A loop end signal fromLoop5 ends the stream.

FIG. 33 also illustrates the generation of Loop0 count. Loop0 countequals the updated data stored in the corresponding working countregister 3311. Loop0 count is updated on each change of working Loop0count register 3311. The loop counts for the higher loops (Loop1, Loop2,Loop3, Loop4 and Loop5) are similarly generated.

FIG. 33 also illustrates the generation of Loop0 address. Loop0 addressequals the data output from multiplier 3313. Loop0 address is updated oneach change of working Loop0 count register 3311. Similar circuits forLoop1, Loop2, Loop3, Loop4 and Loop5 produce corresponding loopaddresses. In this example, Loop0 count register 3311 and the other loopcount registers are implemented as count up registers. In anotherexample, initialization and comparisons operate as count down circuits.

Referring again to FIG. 32, the value of the loop down count, such asLoop0, is given by expression (2).

Loopx/=ICNTx−Loopx  (2)

That is, the loop down count is the difference between the initialiteration count specified in the stream template register and the loopup count produced as illustrated in FIG. 33.

LANE/REMAINING ELEMENTS CONTROL WORD unit 3211 (FIG. 32) generates acontrol word 3213 based upon the number of lanes from NUMBER OF LANESunit 3204 and the loop down count selected by multiplexer 3212. Thecontrol input to multiplexer 3212 is the TRANSPOSE signal from field3002 of FIG. 30. If TRANSPOSE is disabled (“000”), multiplexer 3212selects the Loop0 down count Loop0/. For all other legal values ofTRANSPOSE (“001”, “010”, “011”, “100”, “101” and “110”) multiplexer 3212selects the Loop1 down count Loop1/. The streaming engine maps theinnermost dimension to consecutive lanes in a vector. For normal streamsthis is Loop0. For transposed streams, this is Loop1, becausetransposition exchanges the two dimensions.

LANE/REMAINING ELEMENTS CONTROL WORD unit 3211 generates control word3213 as follows. Control word 3213 has a number of bits equal to thenumber of lanes from unit 3204. If the remaining count of elements ofthe selected loop is greater than or equal to the number of lanes, thenall lanes are valid. For this case, control word 3213 is all ones,indicating that all lanes within the vector length VECLEN are valid. Ifthe remaining count of elements of the selected loop is nonzero and lessthan the number of lanes, then some lanes are valid and some areinvalid. According to the lane allocation described above in conjunctionwith FIGS. 21 and 22, stream elements are allocated lanes starting withthe least significant lanes. Under these circumstances. control word3213 includes a number of least significant bits set to one equal to thenumber of the selected loop down count. All other bits of control word3213 are set to zero. In the example illustrated in FIG. 32, the numberof lanes equals eight and there are five valid (1) least significantbits followed by three invalid (0) most significant bits whichcorresponds to a loop having five elements remaining in the finaliteration.

Control word expansion unit 3214 expands the control word 3213 basedupon the magnitude of LANE SIZE. The expanded control word includes onebit for each minimally sized lane. In this example, the minimum streamelement size, and thus the minimum lane size, is one byte (8 bits). Inthis example, the size of holding registers 2818/2828 equals the vectorsize of 64 bytes (512 bits). Thus, the expanded control word has 64bits, one bit for each byte of stream holding registers 2818/2828. Thisexpanded control word fills the least significant bits of thecorresponding valid register 2819 and 2829 (FIG. 28).

For the case when VECLEN equals the vector length, the description iscomplete. The expanded control word includes bits for all places withinrespective valid register 2819/2829. There are some additionalconsiderations when VECLEN does not equal the vector length. When VECLENdoes not equal the vector length, the expanded control word does nothave enough bits to fill the corresponding valid register 2819/2829. Asillustrated in FIG. 32, the expanded control word fills the leastsignificant bits of the corresponding valid register 2819/2829, thusproviding the valid/invalid bits for lanes within the VECLEN width.Another mechanism is provided for lanes beyond the VECLEN width up tothe data width of stream head register 2818.

Referring still to FIG. 32, multiplexer 3215 and group duplicate unit3216 are illustrated to provide the needed additional valid/invalidbits. Referring to the description of VECLEN, if group duplication isnot enabled (GRDUP=0), then the excess lanes are not valid. A firstinput of multiplexer 3215 is an INVALID 0 signal that includes multiplebits equal in number to VEDLEN. When GRDUP=0, multiplexer 3215 selectsthis input. Group duplicate unit 3216 duplicates this input to allexcess lanes of stream head register 2818. Thus, the most significantbits of valid register 2819 are set to zero indicating the correspondingbytes of stream head register 2818 are invalid. This occurs for vectors1-7 of the example shown in Table 15, vectors 1-14 of the example shownin Table 16, and vectors 1-29 of the example shown in Table 17.

In another example, mux 3215 and group duplicate block 3216 are replacedwith group duplicate logic that is similar to the group duplicate logic2025 illustrated in FIG. 31.

As previously described, if group duplication is enabled (GRDUP=1), thenthe excess lanes of stream head register 2818 (FIG. 28) are filled withcopies of the least significant bits. A second input of multiplexer 3215is the expanded control word from control word expansion unit 3214. WhenGRDUP=1, multiplexer 3215 selects this input. Group duplicate unit 3216duplicates this input to all excess lanes of stream head register 2818.

There are two possible outcomes. In one outcome, in most cases, all thelanes within VECLEN are valid and the bits from control word expansionunit 3214 are all ones. This occurs for vectors 1-7 of the groupduplication example shown in Table 18 and vectors 1-14 of the groupduplication example shown in Table 19. Under these conditions, all bitsof the expanded control word from control word expansion unit 3214 areone and all lanes of stream head register 2818 are valid. Groupduplicate unit 3216 thus fills all the excess lanes with ones. In theother outcome, the number of remaining stream data elements is less thanthe number of lanes within VECLEN. This occurs for vector 8 in the groupduplication example shown in Table 18 and vector 15 in the groupduplication example shown in Table 19. Under these conditions, somelanes within VECLEN are valid and some are invalid. Group duplicate unit3216 fills the excess lanes with bits having the same pattern as theexpanded control word bits. In either case, the excess lanes are filledcorresponding to the expanded control bits.

Referring still to FIG. 32, a boundary 3217 is illustrated between theleast significant bits and the most significant bits. The location ofthis boundary is set by the size of VECLEN relative to the size ofstream head register 2818.

FIG. 34 is a partial schematic diagram 3400 illustrating the streaminput operand coding described above. FIG. 34 illustrates a portion ofinstruction decoder 113 (see FIG. 1) decoding src1 field 1305 of oneinstruction to control corresponding src1 input of functional unit 3420.These same or similar circuits are duplicated for src2/cst field 1304 ofan instruction controlling functional unit 3420. In addition, thesecircuits are duplicated for each instruction within an execute packetcapable of employing stream data as an operand that are dispatchedsimultaneously.

Instruction decoder 113 receives bits 13-17 of src1 field 1305 of aninstruction. The opcode field (bits 3-12 for all instructions andadditionally bits 28-31 for unconditional instructions) unambiguouslyspecifies a corresponding functional unit 3420 and the function to beperformed. In this example, functional unit 3420 can be L2 unit 241, S2unit 242, M2 unit 243, N2 unit 244 or C unit 245. The relevant part ofinstruction decoder 113 illustrated in FIG. 34 decodes src1 bit field1305. Sub-decoder 3411 determines whether src1 bit field 1305 is in therange from 00000 to 01111. If this is the case, sub-decoder 3411supplies a corresponding register number to global vector register file231. In this example, the register number is the four least significantbits of src1 bit field 1305. Global vector register file 231 recallsdata stored in the register corresponding to the register number andsupplies the data to the src1 input of functional unit 3420.

Sub-decoder 3412 determines whether src1 bit field 1305 is in the rangefrom 10000 to 10111. If this is the case, sub-decoder 3412 supplies acorresponding register number to the corresponding local vector registerfile. If the instruction is directed to L2 unit 241 or S2 unit 242, thecorresponding local vector register file is local vector register file232. If the instruction is directed to M2 unit 243, N2 unit 244 or Cunit 245, the corresponding local vector register file is local vectorregister file 233. In this example, the register number is the threeleast significant bits of src1 bit field 1305. The corresponding localvector register file 232/233 recalls data stored in the registercorresponding to the register number and supplies the data to the src1input of functional unit 3420.

Sub-decoder 3413 determines whether src1 bit field 1305 is 11100. Ifthis is the case, sub-decoder 3413 supplies a stream 0 read signal tostreaming engine 125. Streaming engine 125 then supplies stream 0 datastored in holding register 2818 to the src1 input of functional unit3420.

Sub-decoder 3414 determines whether src1 bit field 1305 is 11101. Ifthis is the case, sub-decoder 3414 supplies a stream 0 read signal tostreaming engine 125. Streaming engine 125 then supplies stream 0 datastored in holding register 2818 to the src1 input of functional unit3420. Sub-decoder 3414 also supplies an advance signal to stream 0. Aspreviously described, streaming engine 125 advances to store the nextsequential vector of data elements of stream 0 in holding register 2818.

Supply of a stream 0 read signal to streaming engine 125 by eithersub-decoder 3413 or sub-decoder 3414 triggers another data movement.Upon such a stream 0 read signal, streaming engine 125 supplies the datastored in valid register 2819 to predicate register file 234 forstorage. In accordance with this example, this is a predetermined dataregister within predicate register file 234. In this example, dataregister P0 corresponds to stream 0.

Sub-decoder 3415 determines whether src1 bit field 1305 is 11110. Ifthis is the case, sub-decoder 3415 supplies a stream 1 read signal tostreaming engine 125. Streaming engine 125 then supplies stream 1 datastored in holding register 2828 to the src1 input of functional unit3420.

Sub-decoder 3416 determines whether src1 bit field 1305 is 11111. Ifthis is the case, sub-decoder 3416 supplies a stream 1 read signal tostreaming engine 125. Streaming engine 125 then supplies stream 1 datastored in holding register 2828 to the src1 input of functional unit3420. Sub-decoder 3414 also supplies an advance signal to stream 1. Aspreviously described, streaming engine 125 advances to store the nextsequential vector of data elements of stream 1 in holding register 2828.

Supply of a stream 1 read signal to streaming engine 125 by eithersub-decoder 3415 or sub-decoder 3416 triggers another data movement.Upon such a stream 1 read signal, streaming engine 125 supplies the datastored in valid register 2829 to predicate register file 234 forstorage. In accordance with this example, this is a predetermined dataregister within predicate register file 234. In this example, dataregister P1 corresponds to stream 1.

Similar circuits are used to select data supplied to scr2 input offunctional unit 3402 in response to the bit coding of src2/cst field1304. The src2 input of functional unit 3420 can be supplied with aconstant input in a manner described above. If instruction decoder 113generates a read signal for stream 0 from either scr1 field 1305 orscr2/cst field 1304, streaming engine 125 supplies the data stored invalid register 2819 to predicate register P0 of predicate register file234 for storage. If instruction decode 113 generates a read signal forstream 1 from either scr1 field 1305 or scr2/cst field 1304, streamingengine 125 supplies the data stored in valid register 2829 to predicateregister P1 of predicate register file 234 for storage.

The exact number of instruction bits devoted to operand specificationand the number of data registers and streams are design choices. Inparticular, the specification of a single global vector register fileand omission of local vector register files is feasible. This exampleemploys a bit coding of an input operand selection field to designate astream read and another bit coding to designate a stream read andadvancing the stream.

The process illustrated in FIG. 34 automatically transfers valid datainto predicate register file 234 each time stream data is read. Thetransferred valid data can then be used by P unit 246 for furthercalculation of meta data. The transferred valid data can also be used asa mask or as an operand for other operations by one or more of vectordata path side B 116 functional units including L2 unit 241, S2 unit242, M2 unit 243, N2 unit 244 and C unit 245. There are numerousfeasible compound logic operations employing this stream valid data.

FIG. 35 is a partial schematic diagram 3500 illustrating another exampleconfiguration for selecting operand sources. In this example, therespective stream valid register 2819/2829 need not be automaticallyloaded to a predetermined register in predicate register file 234.Instead, an explicit instruction to P unit 246 is used to move the data.FIG. 35 illustrates a portion of instruction decoder 113 (see FIG. 1)decoding src1 field 1305 of one instruction to control a correspondingsrc1 input of P unit 246. These same or similar circuits can beduplicated for src2/cst field 1304 (FIG. 13) of an instructioncontrolling P unit 246.

Instruction decoder 113 receives bits 13-17 of src1 field 1305 of aninstruction. The opcode field opcode field (bits 3-12 for allinstructions and additionally bits 28-31 for unconditional instructions)unambiguously specifies P unit 246 and the function to be performed. Therelevant part of instruction decoder 113 illustrated in FIG. 35 decodessrc1 bit field 1305. Sub-decoder 3511 determines whether src1 bit field1305 is in the range 00000 to 01111. If this is the case, sub-decoder3511 supplies a corresponding register number to global vector registerfile 231. In this example, the register number is the four leastsignificant bits of src1 bit field 1305. Global vector register file 231recalls data stored in the register corresponding to the register numberand supplies the data to the src1 input of P unit 246.

Sub-decoder 3512 determines whether src1 bit field 1305 is in the range10000 to 10111. If this is the case, sub-decoder 3512 supplies a decodedregister number to the predicate register file 234. In this example, theregister number is the three least significant bits of src1 bit field1305. The predicate register file 234 recalls data stored in theregister corresponding to the register number and supplies the data tothe src1 input of predicate unit 246.

Sub-decoder 3513 determines whether src1 bit field 1305 is 11100. Ifthis is the case, sub-decoder 3513 supplies a stream 0 valid read signalto streaming engine 125. Streaming engine 125 then supplies valid datastored in valid register 2819 to the src1 input of P unit 246.

Sub-decoder 3514 determines whether src1 bit field 1305 is 11101. Ifthis is the case, sub-decoder 3514 supplies a stream 1 valid read signalto streaming engine 125. Streaming engine 125 then supplies stream 1valid data stored in valid register 2829 to the src1 input of P unit246.

The P unit 246 instruction employing the stream valid register 2819/2829as an operand can be any P unit instruction previously described such asNEG, BITCNT, RMBD, DECIMATE, EXPAND, AND, NAND, OR, NOR, and XOR.

The special instructions noted above can be limited to P unit 242. Thus,the operations outlined in FIGS. 34 and 35 can be used together. If thefunctional unit specified by the instruction is L2 unit 241, S2 unit242, M2 unit 243, N2 unit 244 or C unit 245, then src1 field 1305 isinterpreted as outlined with respect to FIG. 34. If the functional unitspecified by the instruction is P unit 246, then src1 field 1305 isinterpreted as outlined with respect to FIG. 35. Alternatively, theautomatic saving of the stream valid register to a predeterminedpredicate register illustrated in FIG. 34 can be implemented in oneexample and not implemented in another example.

BLOCK CACHE MANAGEMENT and PRELOAD OPERATIONS

FIG. 36 illustrates movement of data between various levels of memory inexample system 3600. In this example, processor 100 (FIG. 1) (referredto as “processor A”) is combined with a second processor 3611 (referredto as “processor B”) and each processor is coupled to a block of sharedlevel three (L3) memory 3650 via bus 3651. Processor B includes a blockof unshared level two memory 3612. A direct memory access (DMA) engine3660 may be programmed to transfer blocks of data/instructions from L3memory to L2 memory 130 or L2 memory 3612 using known or later developedDMA techniques. Various types of peripherals 3662 are also coupled tomemory bus 3651, such as wireless and/or wired communicationcontrollers, etc.

In this example, processor A, processor B, L3 memory 3650 are allincluded in a SoC 3600 that may be encapsulated to form a package thatmay be mounted on a substrate such as a printed circuit board (PCB)using known or later developed packaging techniques. For example, SoC3600 may be encapsulated in a ball grid array (BGA) package. In thisexample, external memory interface (EMI) 3652 allows additional externalbulk memory 3654 to be accessed by processor A and/or processor B.

In this example, processor B is an ARM® processor that may be used forscalar processing and control functions. In other examples, varioustypes of known or later developed processors may be combined with DSP100. While two processors are illustrated in this example, in anotherexample, multiple copies of DSP 100 and/or multiple copies of processorB may be included within an SoC and make use of the block cachemanagement operations (CMO) described hereinbelow in more detail.

The complex interrelation of parts of digital signal processor system3600 permits numerous data movements. First, L1 instruction cache 121may receive instructions recalled from L2 unified cache 130 for a cachemiss fill. In this example, there is no hardware support forself-modifying code so that instructions stored in L1 instruction cache121 are not altered and therefore do not require write-back. There aretwo possible data movements between L1 data cache 123 and L2 unifiedcache 130. The first of these data movements is a cache miss fill fromL2 unified cache 130 to L1 data cache 123. Data may also pass from L1data cache 123 to L2 unified cache 130. This data movement takes placefor several reasons, such as: a write miss to L1 data cache 123 whichmust be serviced by L2 unified cache 130; a victim eviction from L1 datacache 123 to L2 unified cache 130; and a snoop response from L1 datacache 123 to L2 unified cache 130. Data can be moved between L2 unifiedcache 130 and level 3 (L3) memory 3650. This can take place for severalreasons, such as: a cache miss to L2 unified cache 130 service from L3memory 3650, or a direct memory access 3660 data movement from L3 memory3650 and L2 unified cache 130 configured as SRAM; a victim eviction fromL2 unified cache 130 to L3 memory 3650, or a direct memory access 3660data movement from a portion of L2 unified cache 130 configured as SRAMto L3 memory 3650. Finally, data can move between L2 unified cache 130and peripherals 3662. These movements take place for several reasons,such as: a direct memory access 3660 data movement from peripheral 3662and L2 unified cache 130 configured as SRAM; or a direct memory access3660 data movement from a portion of L2 unified cache 130 configured asSRAM to peripherals 3662. Data movement between L2 unified cache 130 andL3 memory 3650 and between L2 unified cache 130 and peripherals 3662employ data transfer bus 3651 and may be controlled by direct memoryaccess unit 3660. These direct memory access data movements may takeplace as result of a command from central processing unit core 110 or acommand from another digital signal processor system.

The number and variety of possible data movements within digital signalprocessor system 3600 makes the problem of maintaining coherencedifficult. In any cache system data coherence is a problem. The cachesystem attempts to control data accesses so that each cache returns themost recent data. As an example in a single level cache, a readfollowing a write to the same memory address maintained within the cachemust return the newly written data. This coherence should be maintainedregardless of the processes within the cache. This coherence preservesthe transparency of the cache system. That is, the programmer need notbe concerned about the data movements within the cache and can programwithout regard to the presence or absence of the cache system. Thistransparency feature is important if the data processor is to properlyexecute programs written for members of a data processor family havingno cache or varying amounts of cache. Typically, it is preferable thatthe cache hardware maintain the programmer illusion of a single memoryspace. An example of an ordering hazard is a read from a cache line justvictimized and being evicted from the cache. Another example in anon-write allocate cache is a read from a cache line following a writemiss to that address with the newly written data in a write bufferwaiting write to main memory. In the current examples, the cache systemincludes hardware to detect and handle such special cases.

In the example DSP processor 100 (FIG. 1) and the example DSP system3600, a second level L2 cache introduces additional hazards. Coherenceshould be maintained between the levels of cache no matter where themost recently written data is located. Generally, L1 data cache willhave the most recent data while the higher level L2 cache may have olddata. If an access is made to the L2 cache the cache system mustdetermine if a more recent copy of the data is stored in the lower levelL1D cache. This generally triggers a snoop cycle in which the L2 cachepolls the L1D cache for more recent data before responding to theaccess. A snoop is nearly like a normal access to the snooped cacheexcept that snoops are generally given higher priority. Snoops aregranted higher priority because another level cache is stalled waitingon the response to the snoop. If the data stored in the lower level L1Dcache has been modified since the last write to the higher level L2cache, then this data is supplied to the higher level L2 cache. This isreferred to as a snoop hit. If the data stored in the lower level L1Dcache is clean and thus has not been changed since the last write to thehigher level L2 cache, then this is noted in the snoop response but nodata moves. In this case the higher level L2 cache stores a valid copyof the data and can supply this data.

Additional hazards with a two-level cache include snoops to a lowerlevel cache where the corresponding data is a victim being evicted, andsnoops to data during a write miss in the lower level cache fornon-write allocation systems which places the data in a write buffer. L2unified cache 130 may need to evict a cache entry which is also cachedwithin L1 instruction cache 121 or L1 data cache 123. A snoop cycle isrequired to ensure the latest data is written out to the external mainmemory. A write snoop cycle is transmitted to both L1 instruction cache121 and L1 data cache 123. This write snoop cycle misses if this data isnot cached within the L1 caches. L1 data cache 123 reports the snoopmiss to L2 unified cache 130. No cache states within L1 data cache 123are changed. Upon receipt of the snoop miss report, L2 unified cache 130knows that it holds the only copy of the data and operates accordingly.If the snoop cycle hits a cache entry within L1 data cache 123, theresponse differs depending on the cache state of the corresponding cacheentry. If the cache entry is not in a modified state, then L2 unifiedcache 130 has a current copy of the data and can operate accordingly.The cache entry is invalidated within L1 data cache 123. It isimpractical to maintain cache coherency if L1 data cache 123 caches thedata and L2 unified cache 130 does not. Thus, the copy of the dataevicted from L2 unified cache 130 is no longer cached within L1 datacache 123. It should be understood that when an entry is invalidated ata given level of cache, while it is no longer available and therefore nolonger cached within that level of cache, the data may still be presentuntil it is overwritten by a later cache fetch. If the cache entry in L1data cache 123 is in a modified state and thus had been modified withinthat cache, then the snoop response includes a copy of the data. L2unified cache 130 must merge the data modified in L1 data cache 123 withdata cached within it before eviction to external memory. The cacheentry within L1 data cache 123 is invalidated.

In a similar fashion snoop cycles are sent to L1 instruction cache 121.In this example, DSP system 100 cannot modify instructions within L1instruction cache 121, therefore no snoop return is needed. Upon a snoopmiss nothing changes within L1 instruction cache 121. If there is asnoop hit within L1 instruction cache 121, then the corresponding cacheentry is invalidated. A later attempt to fetch the instructions at thataddress will generate a cache miss within L1 instruction cache 121. Thiscache miss will be serviced from L2 unified cache 130.

As mentioned above, it is desirable to provide a level of control to theprogrammer over cache operations. In this example, the cache systemsupports a writeback mechanism, whereby the programmer can direct the L2cache 130 to write a block of data in the L2 cache back to external L3shared memory 3650 for shared access by processor B 3611 which doesn'thave access to the L2 cache 130. Similarly, it is often desirable to beable to clear or invalidate L2 cache entries so that new data can beaccessed at addresses which have been updated in the shared memory 3650.

In this example, in addition to its core data stream support, thestreaming engine 125 supports a range of special “data-less” streams. Adata-less stream may be used to move data between various levels ofcache and memory, without bringing data to the processor. In thisexample, two special instructions are provided to allow a program toinitiate a data-less stream. A block cache maintenance operation isinitiated by a “BLKCMO” instruction. A block cache preload operation isinitiated with a “BLKPLD” instruction.

Examples of prior cache writeback and invalidate mechanisms haverequired the programmer to perform multiple accesses to controlregisters to perform programmer directed cache operations. For example,if the programmer wishes to remove (evict) four lines in the cache, awrite to four control register bits is normally required. In systemswhich implement a control register on which programmer directed cacheoperations are based, four writes must be performed. The programmer mustprovide program code to track the address between each write. Whilethese methods are functional, they are costly in terms of softwareoverhead. These methods generally require the programmer to have anunderstanding of the underlying cache architecture parameters. Suppose ablock of 128-bytes is to be copied back to memory. If the cachearchitecture has a 32-byte line size, then four writes must be performedto order this writeback. If the cache architecture has a 64-byte linesize cache, then only two writes are necessary. This prior approachnatively inhibits the portability of instruction code that controls thecache.

In another example approach described in more detail in U.S. Pat. No.6,665,767 to David A. Comisky et al., a program-controlled cachemanagement technique employs an address and word count memory mappedcontrol register structure. While this method is functional, it requiressoftware overhead to correctly program the memory mapped controlregisters.

FIG. 37 is a partial schematic diagram for cache management operationsusing a streaming stream engine, such as streaming engine 125 which isshown in more detail FIG. 28. As described hereinabove, processor 100includes a streaming engine 125 that includes two independent streamengines 2810, 2820 that can each be programmed to fetch streams of datafrom the L2 unified cache/memory and provide them to processor core 110for consumption. In this example, stream engine 2810 includes mode logic3740 to allow stream engine 2810 to execute in data-less mode. Asdescribed hereinabove in more detail, address generator 2811 may beprogrammed to generate a simple or complex stream of addresses.

In this example, in addition to its core data stream support, thestreaming engine 2810 supports a range of special data-less streams. Adata-less stream may be used move data between various levels of cacheand memory, without bringing data to the processor. In this example, twospecial instructions are provided to allow a program to initiate adata-less stream. A block cache maintenance operation is initiated by a“BLKCMO” instruction. A block cache preload operation is initiated witha “BLKPLD” instruction.

In this example, block cache management operations may be performedunder control of a software program being executed by processor 100using a software instruction referred to herein as a “block cachemanagement operation” (BLKCMO) instruction. The BLKCMO instruction isfetched and decoded by the instruction pipeline of processor 100 asdescribed hereinabove in more detail. After being decoded, a BLKCMOinstruction is then “executed” using the streaming engine to provide astream of addresses, that may be referred to as a “block of addresses,”to the L2 cache 130 to clean and/or invalidate a block of memoryaddresses that may or may not be present in the L2 cache 130.

Cache maintenance operations move cache lines out of cache levels nearerto the processor to cache levels that are further from the processor.This allows the programmer to manually manage when data leaves theprocessor's caches. While the programmer is generally abstracted fromthe underlying cache architecture of the cache, the programmer isgenerally aware of the required accesses that instruction code mustperform and the memory usage of the process. Consequently, theprogrammer is aware of the cache cycles that are required for particularcode segments. Thus, a good solution to cache control is to provide theprogrammer direct address and word count control for programmer directedcache cycles using a BLKCMO instruction. This is in contrast torequiring knowledge about the cache parameters such as line size,associativity, replacement policies, etc. of prior techniques.

In this example, the format of a BLKCMO instruction is similar toinstruction format 1300 (FIG. 13). The assembler syntax is: BLKCMO src1,src2(cst), src3. Source 1 is the starting base address contained in aregister encoded in the src1 field 1305, source 2 is a 5-bit constantand is encoded as shown in Table 30 in the src2 field 1304, and source 3specifies the number of bytes involved in the maintenance operation.Source 3 is a 32-bit value specified by a register encoded in dst field1303.

TABLE 30 BLKCMO opcodes 0x10 Data Cache Clean to the point ofUnification, Shareable 0x11 Data Cache Clean and Invalidate to the pointof Unification, Shareable 0x12 Data Cache Invalidate to the point ofUnification, Shareable 0x13 Data Cache Clean to the point of Coherence,Shareable 0x14 Data Cache Clean and Invalidate to the point of Coherence0x15 Data Cache Invalidate to the point of Coherence, Shareable 0x16RESERVED 0x17 RESERVED 0x18 Data Cache Clean to Point of Unification,Non-Shareable 0x19 Data Cache Clean and Invalidate to the point ofUnification, Non-Shareable 0x1A Data Cache Invalidate to the point ofUnification, Non-Shareable 0x1B Data Cache Clean to the point ofCoherence, Non-Shareable 0x1C Data Cache Clean and Invalidate to thepoint of Coherence 0x1D Data Cache Invalidate to the point of Coherence,Non-Shareable 0x1E RESERVED 0x1F RESERVED

Referring still to FIG. 37, L2 cache 130 includes multiple cache lines3731 that each include a tag field 3732 and a data element field 3733for holding data that has been fetched from higher level L3 memory 3650(FIG. 36). Tag field 3732 includes address bits to specify the physicaladdress from which the respective data elements were fetched in L3memory. Tag field 3732 also includes status bit that identify the statusof the respective data field, such as “clean,” and “valid.” A valid tagbit means the respective data field has been loaded with data elementfetched from L3 memory. A clean tag bit means the data elements have notbeen modified by processor 100 since they were fetched from L3 memory.

Snoop logic 3734 performs the various snoop operations describedhereinabove whenever an access is made to L2 cache 130 that may requirea data update. Snoop logic 3734 performs the same snoop operationsirrespective of whether an L2 access is being made by processor 100 viarequest bus 3735 or by streaming engine 2810 via L2 interface 2833.Therefore, essentially no additional control logic is needed to supportthe block CMO instructions described herein.

Streaming engine 2810 treats Clean and Clean-Invalidate operations asequivalent to reads. That is, the Clean or Clean-Invalidate command mayproceed as long as the address range is readable by the currentprivilege level. Control signal “CMO” 3743 is asserted to L2 cache 130to inform it that it does not need to provide the read data requested bythe CMO clean operations. The streaming engine treats Invalidateoperations as equivalent to writes. Control signal “CMO” is asserted toL2 cache 130 to inform it that it will not be receiving any write datawith the CMO invalidate operation. The Invalidate commands may proceedonly if the address range is writable by the current privilege level.For a Clean operation, L2 cache 130 writes back any updates to the linethat have not yet been sent to L3 memory. For an Invalidate operation,L2 cache 130 marks the line invalid and thereby removes it from thecache. For a Clean-Invalidate operation, L2 cache 130 writes back anyupdates to L3 memory and then marks the line invalid and thereby removesit from the cache.

If the streaming engine detects a privilege violation, it signals afault and halts the block CMO.

Referring again to Table 30, the “point of unification” is the level inthe cache hierarchy where instruction and data streams meet. The “pointof coherence” is the level in the cache hierarchy where all masters seethe updated data. In this example, the point of unification is the L2unified memory 130. The point of coherence is the L3 memory 3650 (FIG.36) that is shared by processor A 100 and processor B 3611 (FIG. 36).

Not all memory types support cache maintenance operations. If a programissues cache maintenance operations on unsupported memory types, thestreaming engine may either discard the CMOs or signal an exceptionsimilar to a privilege violation. For example, any CMOs to memory typemarked as “System/Device” memory type as returned by the μTLB 2812 wouldbe an error and the streaming engine would drop the command from beingsent into the memory system and return an error to the processor on theread status packet.

In this example, the streaming engine supports a “fencing” mechanismbetween outstanding processor stores to L1D data cache which preventsthe streaming engine from sending requests into the system until theoutstanding stores from processor core 110 (FIG. 36) have landed. Afence is initiated by executing an “MFENCE” instruction on processorcore 110. Execution of the MFENCE instruction is accomplished viainternal signaling between the processor core 110, L1D 123, andstreaming engine 125. This fencing check is done on any new openedstreams issued by processor 110. Upon receiving a stream open, thestreaming engine starts its address generation and μTLB lookups, andprepares the request to go out. Once the request reaches the arbitrationunit, the commands are stalled until the fence is complete. This isaccomplished by monitoring the IDLE signal 3742 from L1D 123 indicatingthe pertinent stores have completed. This prevents streaming engine 2810from receiving old or stale data. The streaming engine asserts aseparate coherence active signal 3741 to the processor indicatingwhether any CMO stream commands are still active in the system. Itasserts this signal regardless of whether the CMO stream that generatedthose commands is active, frozen or inactive. The processor's MFENCEinstruction waits for this signal to be deasserted, indicating that alloutstanding CMO operations have completed. This may be necessary whenclosing a block CMO stream early, or during context switches.

In this example, the format of a BLKPLD instruction is similar toinstruction format 1300 (FIG. 13). The assembler syntax is: BLKPLD src1,src2(cst), src3. Source 1 is the starting base address contained in aregister encoded in the src1 field 1305, source 2 is a 5-bit constantand is encoded as shown in Table 31 in the src2 field 1304, and source 3specifies the number of bytes involved in the maintenance operation.Source 3 is a 32-bit value specified by a register encoded in dst field1303.

TABLE 31 BLKPLD opcodes 0x10 Preload to L3 cache for read 0x11 Preloadto L3 cache for write 0x12 Preload to L2 cache for read 0x13 Preload toL2 cache for write 0x14-1F Reserved

Preload to L3 Cache attempts to bring data to a cache level outsideprocessor 100 (FIG. 36), such as L3 memory 3650. The goal is to ensuredata is on-chip within SoC 3600, even if it is not yet in L2 130. Thisis potentially useful for large data sets that do not fit within the L2memory.

Preload to L2 Cache attempts to bring data to the L2 cache 130 withinprocessor 100. This is potentially useful for data sets that do fitwithin L2 cache 130.

Preload for Read indicates that the processor intends to read the data,but not necessarily write it. The streaming engine requests sharedaccess to the data, allowing other caches to retain copies of the dataif they already have copies.

Preload for Write indicates that the processor intends to write to thepreloaded block. The streaming engine requests exclusive access to thedata, with the intent of removing copies from other caches. This reducesthe cost of subsequent processor writes to those lines.

The streaming engine 2810 treats all preload requests as reads,including Preload for Write. If a privilege check fails, the streamingengine silently ignores it. It drops the faulted preload command andcontinues with the block preload operation.

The streaming engine only sends preload requests for normal, cacheablememory. It silently drops preload requests for other memory types.Preload instructions serve as a hint to the caches. Caches may ignorethe hint.

FIG. 38 is a flow diagram illustrating operation of the cache managementoperations using streaming engine 125. In this example, data-lessstreams reuse the hardware 2810 for stream engine 0 to perform theiractions. Therefore, stream 0 must be inactive when issuing a data-lessstream instruction (e.g., it must not be in the process of streaming adata stream as described hereinabove).

At 3800, a program executes an BLKCMO stream instruction to open adata-less stream. The streaming engine begins issuing requests to thememory system. Starting a data-less stream asserts the task stateregister SE0 bit (TSR.SE0), as described hereinabove in more detail. Thestreaming engine asserts to the processor a coherence active signal 3741(FIG. 37) which processor 100 (FIG. 1) can monitor to determine that anactive cache management operation is in progress. The streaming enginewill deassert the coherence active signal 3741 when all coherencecommands associated with the data-less streams sent have returned.TSR.SE0 remains asserted until the program issues a SECLOSE for stream0. If the program issues a SECLOSE before the data-less streamcompletes, the streaming engine stops issuing requests to the memorysystem.

Programs can synchronize with a data-less stream by reading from it witha reference to *SE0 or *SE0++ (see FIG. 34). The streaming engine willbegin returning empty data-phases to the processor once it has issuedall the commands associated with the stream, and those commands have allcompleted. The streaming engine will report any errors encountered inthe fault status associated with these data-phases.

For example, in this example the stream of addresses used for performingthe block CMO is a stream of virtual addresses in a virtual addressspace of the processor. As described above in more detail, μTLB 2812(FIG. 37) converts a single 48-bit virtual address to a 44-bit physicaladdress each cycle. If a needed virtual address entry is not in theμTLB, then an exception is generated and a new table entry is determinedby a software process. In this manner, the stream of virtual addressesis translated into a respective stream of physical addresses forperforming the block CMO on the cache.

In some cases, the μTLB and associated control software/firmware maydetermine that at least one physical address of the stream of physicaladdresses is an invalid address. In this case, an exception is generatedto notify the processor that an invalid address has been determined.

As will be described in more detail below, in some examples a page faultmay occur during a block CMO operation. In this case, an exception isgenerated to notify the processor that a page fault has been detected.

In some examples, a process environment may be created by the operatingsoftware or other control software or firmware to define access rightsfor a particular software task or section of instruction code. This maybe based on task numbers, for example. In this case, when a block CMOoperation is performed, a check may be performed to determine whetherthe current process has access rights to the memory at the stream ofphysical addresses. If the current process does not have access rights,then an error is returned when the block CMO is attempted.

At 3801 the processor attempts to read a single data element from thestream. At 3802, this stalls the processor until the streaming enginefinishes issuing the commands for the data-less stream, and the memorysystem completes all the commands. The stall occurs because thestreaming engine will return an empty data phase with error status, ifany, while the CMO progresses. No data is returned because this is a“data-less” operation.

At 3803, the processor can check the error status bus and fault statusregister and decide how to proceed if an error is received. As describedabove for various examples, errors for various conditions may bedetected, such as an invalid address, a page fault, a lack of accessrights, etc. At 3804, the processor may save and restore the data-lessstream after it has corrected errors.

At 3805, the program can execute a SECLOSE for stream 0. TSR.SE0 isdeasserted to 0, indicating TSR.SE0 is inactive. Optionally, a programmay issue a SEOPEN without a SECLOSE for a new stream while a data-lessstream is active. The processor would stall any new commands inside theprocessor until the data-less stream is done, as indicated by thestreaming engine via the coherence active signal 3741.

At 3806, these steps can be spread out in a program allowing othercomputation to occur in parallel with the data-less stream. Inparticular, a program may do significant other work between 3800 and3801.

At 3807, the program may execute a SEOPEN stream instruction on SE0 tocause a stream of data elements to be fetched by the streaming engineand to be presented to the processor, as described hereinabove in moredetail.

At 3808, the processor may consume the data elements in the data streamas they are provided by the streaming engine.

At 3809, the processor may execute a SECLOSE instruction to close thedata stream.

In this manner, an autonomous streaming processor, such as streamingprocessor 125 (FIG. 1), may be used in two different modes. In a firstmode illustrated at 3807-3809, a stream of data elements may be fetchedby the streaming engine and presented to a processor for consumption bythe processor. In a second mode illustrated at 3800-3805, the streamingengine may be operated in data-less mode to perform a block cachemanagement operation. This allows a program to manage a cache by simplyexecuting a single stream instruction with operands to specify astarting address and length of a block of addresses. The same addressgeneration hardware is used in both modes of operation, therefore thehardware cost for providing block cache management is minimal.

The block cache management operation technique described hereinabovethat reuses the streaming engine hardware provides a preemptivecoherence vs a reactionary coherence. This reduces snoop overheadwithout requiring complex and expensive cache coherence hardware. Asdescribed herein, a block cache management operation can be initiated onthe streaming engine by executing a single block CMO instruction on theprocessor that is coupled to the streaming engine.

The block cache preload operation technique described hereinabove thatreuses the streaming engine hardware provides a preemptive cache loadthat may reduce cache misses for a block of data. As described herein, ablock cache preload operation can be initiated on the streaming engineby executing a single block preload instruction on the processor that iscoupled to the streaming engine

Page Faults

In another example, a system that performs block cache maintenanceoperations as described herein may also manage a large amount of dataand/or instructions using page faults. A page fault is a type ofexception raised by computer hardware when a running program accesses amemory page that is not currently mapped by the memory management unit(MMU) into the physical address space of a process. Valid page faultsare not errors per se, and are used to increase the amount of memoryavailable to programs in any operating system that utilizes virtualmemory, such as: Microsoft Windows, Unix-like systems (including macOS,Linux, *BSD, Solaris, AIX, and HP-UX), z/OS, etc.

Logically, the page may be accessible to the process, but requires amapping to be added to the process page tables and may additionallyrequire the actual page contents to be loaded from a backing store suchas a disk, a large solid-state memory, or other type of bulk memory. Theexception handling software that handles page faults is generally a partof the operating system kernel. When handling a page fault, theoperating system generally tries to make the required page accessible ata location in physical memory or terminates the program in case of anillegal memory access.

The operating system may delay loading parts of a program from bulkmemory until the program attempts to use it and a page fault isgenerated. The page fault handler in the OS needs to find a freelocation: either a free page in memory, or a non-free page in memory.The latter might be used by another process, in which case the OS needsto write out the data in that page (if it has not been written out sinceit was last modified) and mark that page as not being loaded in memoryin its process page table. Once the space has been made available, theOS can read the data for the new page into memory, add an entry to itslocation in the memory management unit, and indicate that the page isloaded. Thus, page faults add storage access latency to the interruptedprogram's execution.

In such an example, a page fault may occur while a block CMO is inprogress. In that case, the hardware captures the necessary state tosupport resuming a block CMO after a fault. The processor therefore hasthe ability to resume a block CMO operation after a page fault conditionhas been remedied by software. This makes the block CMO more efficient,as it does not require pinning the corresponding pages in memory.Software can assume the block CMO is safe to issue without explicitlynegotiating with the operating system to ensure the pages are presentthroughout the lifetime of the block CMO.

For example, referring again to FIG. 36, assume processor A 100 andprocessor B 3611 participate in a distributed virtual memory (DVM)protocol. At some point, software on processor A 100 (FIG. 36) decidesto writeback-invalidate a large block CMO of data from L2 cache 130(FIG. 36). Meanwhile processor B 3611 (FIG. 36) decides to move one ofthe pages in the middle of that block to a different physical address.Software on processor B 3611 may perform a sequence similar to thatshown in Table 32. In this example, a “data synchronization barrier”(DSB) instruction executed by processor B 3611 causes processor B 3611to stall until execution of all prior instructions are completed.

TABLE 32 page replacement 1 - Mark the page read-only in the page table.2 - Issue an appropriate data sync barrier (DSB) and TLB invalidate DVM,data sync barrier. 3 - Copy the data from the old physical page to thenew physical page. 4 - Mark the page as invalid. 5 - Issue data syncbarrier, TLB invalidate DVM, data sync barrier. 6 - Mark the page asvalid, pointing to the new physical page. 7 - Issue one last data syncbarrier, TLB invalidate DVM, data sync barrier.

If processor A's block CMO races with processor B's performing thesequence of Table 32, processor A has the opportunity to see an invalidpage mapping. At that point, processor A needs to perform a higher-levelsynchronization with processor B in software to know when the page isvalid again so that processor A can resume. This is typicallyimplemented through a page lock mechanism. The SESAVE instruction can beused to store the state of the pending block CMO so that it can berestarted after the page fault is corrected using a SERSTR instruction.

Note that if processor A did actually race with processor B in a DVMremap as shown in Table, 32, a corresponding portion of the block CMOmay end up not being useful due to the page-copy performed by processorB. However, the program on processor A issuing the block CMO can remainoblivious to those machinations and still be correct in all cases byrestarting the block CMO when processor B has completed the remap, whilealso being efficient in the most common case. The block CMO can berestarted using the state information that was saved when the page faulterror was detected.

Other Examples

In described examples, a streaming engine is used to process a data-lessstream that causes a coherence operation to be performed on a designatedhierarchical level of memory without providing stream data to theprocessor. A cache or bulk memory at a designated memory level may bepreloaded for later access by the processor. Similarly, a block ofmemory addresses in a cache may be cleaned and/or invalidated by thedata-less stream operation.

In described examples, a complex DSP processor with multiple functionunits and dual data paths is described. In another example, a simplerDSP that is coupled to a stream processor may be used. In anotherexample, other types of known or later developed processors may becoupled to a stream processor, such as a reduced instruction setcomputer (RISC), a traditional microprocessor, etc.

In described examples, a complex autonomous streaming engine is used toretrieve a data-less stream of data elements. In another example,another type of streaming engine may be used, such as a simple directmemory access device. In another example, the streaming engine may be asecond processor that is programmed to access data autonomously from theprocessor that is consuming the data.

In another example, the system may be designed to allow block CMOinstructions to extend across caches associated with other processors inthe system, such as L2 cache 3612 (FIG. 36) that is owned by processor B3611 (FIG. 36).

In described examples, a processor that consumes a stream of data and astreaming engine that retrieves the stream of data from system memoryare all included within a single integrated circuit (IC) as a system ona chip. In another example, the processor that consumes the stream ofdata may be packaged in a first IC and the streaming engine may bepackaged in a second separate IC that is coupled to the first IC by aknown or later developed communication channel or bus.

In this description, the term “couple” and derivatives thereof mean anindirect, direct, optical, and/or wireless electrical connection. Thus,if a first device couples to a second device, that connection may bethrough a direct electrical connection, through an indirect electricalconnection via other devices and connections, through an opticalelectrical connection, and/or through a wireless electrical connection.

Modifications are possible in the described examples, and other examplesare possible, within the scope of the claims.

1. A method of managing a cache in a computer system, the methodcomprising: executing instructions including a first stream instructionand a second stream instruction on a processor within the computersystem; fetching a stream of data elements from a memory coupled to theprocessor using a stream of addresses generated in a first mode ofoperating a streaming engine in response to executing the first streaminstruction; and performing a block cache management operation (CMO) onthe cache using a block of addresses generated in a second mode ofoperating the streaming engine in response to executing the secondstream instruction.
 2. The method of claim 1, wherein the second streaminstruction includes an opcode to define a type of block CMO andspecifies an operand to define a beginning address of the block ofaddresses.
 3. The method of claim 2, wherein the type of block CMO is acache clean operation for the block of addresses.
 4. The method of claim2, wherein the type of block CMO is a cache clean and invalidateoperation for the block of addresses.
 5. The method of claim 2, whereinthe type of block CMO is a cache invalidate operation for the block ofaddresses.
 6. The method of claim 2, wherein the cache of the computersystem has at least two hierarchical levels of memory; and whereinperforming the block CMO operates on a hierarchical level of memory ofthe cache specified by the opcode.
 7. The method of claim 2, furthercomprising: asserting a status signal by the streaming engine toindicate a block CMO is being performed and de-asserting the statussignal to indicate the block CMO is complete; and executing aninstruction by the processor that causes the processor to wait until theblock CMO is complete.
 8. The method of claim 1, wherein the block ofaddresses used for performing the block CMO is a block of virtualaddresses in a virtual address space of the processor; and furthercomprising: determining if there is a respective valid physical addressin the computer system for each virtual address of the block of virtualaddresses; and translating the block of virtual addresses to arespective block of physical addresses for performing the block CMO onthe cache.
 9. The method of claim 1, wherein executing the second streaminstruction is executed within a current process environment on theprocessor; further comprising determining whether the current processhas access rights to the memory at the block of addresses, and if notreturning an error.
 10. The method of claim 1, further comprising:determining that at least one address of the block of addresses is aninvalid address; and notifying the processor when an invalid address isdetermined.
 11. The method of claim 8, further comprising: detectingthat at least one address of the block of physical addresses causes apage fault; and notifying the processor when a page fault is detected.12. The method of claim 11, further comprising: saving a current stateof the block CMO when a page fault is detected; moving a new page ofdata into the memory; and restarting the block CMO using the savedcurrent state of the block CMO.
 13. A data processing system comprising:a processor to execute instructions including a first stream instructionand a second stream instruction; a memory system coupled to theprocessor, the memory system having a cache with cache lines to storedata elements and a sharable bulk memory storage; and a streaming enginecoupled to the processor and to the memory system, the streaming enginehaving an address generator to generate a stream of addresses and atleast two modes of operation responsive respectively to the first streaminstruction and to the second stream instruction, such that thestreaming engine is operable to use the stream of addresses to fetch arespective stream of data elements from the memory system for access bythe processor in a first mode of operation, and is operable to use thestream of addresses to perform a block cache management operation on thecache in a second mode of operation.
 14. The data processing system ofclaim 13, wherein the block cache management operation is a cache cleanoperation for the stream of addresses.
 15. The data processing system ofclaim 13, wherein the block cache management operation is a cache cleanand invalidate operation for the stream of addresses.
 16. The dataprocessing system of claim 13, wherein the block cache managementoperation is a cache invalidate operation for the stream of addresses.17. The data processing system of claim 13, wherein the memory systemhas at least two hierarchical levels of caches; and wherein performingthe block cache management operation operates on a particularhierarchical level of the caches of the memory system specified by anopcode of the second stream instruction.
 18. The data processing systemof claim 13, wherein the stream of addresses is a stream of virtualaddresses in a virtual address space of the processor; and furthercomprising a micro table look-aside buffer coupled to the addressgenerator to convert the stream of virtual addresses into a stream ofphysical address to perform the block cache management operation.
 19. Amethod for operating a streaming engine in a computer system, the methodcomprising: generating a stream of addresses using an address generatorin the streaming engine; fetching a stream of data elements from a cachein a memory system of the computer system using the stream of addressesand providing the stream of data elements to a processor of the computersystem while the streaming engine is in a first mode of operation; andcleaning the cache by reading the stream of data elements from the cachewithout providing the stream of data elements to the processor while thestreaming engine is in a second mode of operation.
 20. The method ofclaim 19, wherein the stream of addresses is a stream of virtualaddresses in a virtual address space of the processor; and furthercomprising: translating the stream of virtual addresses to a respectivestream of physical addresses; and generating a fault if there is not arespective valid physical address in the computer system for eachvirtual address of the stream of virtual addresses.